Category: Class 8

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 3 Matter Around Us

AP State Syllabus 8th Class Physical Science Important Questions 3rd Lesson Matter Around Us

8th Class Physical Science 3rd Lesson Matter Around Us 1 Mark Important Questions and Answers

Question 1.
What is CNG?
Answer:
CNG means Compressed Natural Gas.

Question 2.
Does the smoke of incense stick diffuse in a room without air?
Answer:
Smoke of incense stick is a gas. Gas diffuses in air only. So the smoke cannot diffuse in the absense of air.

Question 3.
Write decreasing order of the distance between the atoms of solid, liquid and gas.
Answer:
Gas > Liquid > Solid.

Question 4.
What is the temperature where water expands?
Answer:
When temperature is reduced from 4°C to 0°C, water expands instead of compression.

Question 5.
What is dry ice?
Answer:
Solid carbon dioxide is called dry ice.

Question 6.
What is Kelvin scale equivalent to 0°C?
Answer:
273 K.

Question 7.
What are the factors influencing the change in state of a matter?
Answer:

1. Temperature
2. Pressure.

Question 8.
What is humidity?
Answer:
The amount of water vapour present in air is known as humidity.

Question 9.
What is meant by sublimation?
Answer:
When a substance is heated its state changes from solid to vapour directly without changing into liquid. This is called sublimation.

Question 10.
How do acquatic animals and plants survive under water?
Answer:
The gases like oxygen and carbon dioxide will diffuse in water. The acquatic animals under water will survive by inhaling these gases.

Question 11.
What are the different states of matter?
Answer:
Matter exists in three states. They are solids, liquids and gases.

Question 12.
Why are the liquids called fluids?
Answer: Liquids can flow easily from one container to another. Hence they are called fluids.

Question 13.
Why is the solid carbon dioxide called dry ice?
Answer:

1. Solid carbon dioxide converts directly into gaseous state when the pressure is decreased to 1 atmosphere.
2. Due to this reason solid carbon dioxide is also known as dry ice.

Question 14.
Why is the rate of diffusion in gases high?
Answer:
The rate of diffusion in gases is very high than liquids and gases, because

1. Higher speed of gas particles.
2. Greater space between the particles of gas.

Question 15.
Which will decide the change of state of substance?
Answer:
Pressure and temperature decides the state of the substance.

Question 16.
What is the principle involved in ice skating?
Answer:
Pressure is applied on ice with skating boots. As the pressure increases melting point ice decreases. So ice melts at a lower temperature than 0°C. Therefore skating is possible on ice.

Question 17.
What is compression?
Answer:
The volume of gas can be decreased by applying pressure. This process is called compression.

Question 18.
What are fluids?
Answer:
The substances which can flow from one place to other place are called fluids. Generally liquids and gases are fluids.

8th Class Physical Science 3rd Lesson Matter Around Us 2 Marks Important Questions and Answers

Question 1.
What is matter? Give some examples from your day-to-day life.
Answer:
Anything in this world that occupies space and has mass is considered as matter. Examples:
The water we drink, our food, clothes, chairs, tables, air we breath, etc. are the examples of matter.

Question 2.
Compare the following properties of solids, liquids and gases,
a) Shape b) Volume c) Compressibility d) diffusion
Answer:

Property	Solid	Liquid	Gas
Shape	Fixed	Attains the shape of container	No shape
Volume	Fixed	Fixed	No fixed volume
Compressibility	Very less	Intermediate	Maximum
Diffusion	Minimum	Intermediate	Maximum

Question 3.
Give the order of rate of diffusion in solids, liquids and gases.
Answer:
The order of rate of diffusion in solids, liquids and gases is
Gases > Liquids > Solids (or) Solids < Liquids < Gases

Question 4.
Give some experiences with evaporation in your daily life.
Answer:

1. We feel cooler after sweating.
2. Drying of wet clothes when exposed to the sun.
3. Paddy, cereals, etc. will be exposed to the sun to remove moist.
4. Water stored in earthen pots is cooler than the water stored in a metal pot.
5. Fog, which is formed early in the morning during winter season will disappear after sunrise.

Question 5.
Why do we feel cool when nail polish is applied to nails?
Answer:
Nail polish contains acetone which absorb heat energy from our body and evaporates. So the body temperature decreases. So we feel cool when nail polish applied to nails.

Question 6.
Why do we store water in earthen pots?
Answer:
The earthen pots have small pores in it. From that pores water tends to evaporates by gaining heat energy from the pot. So water in pots is cool. So water is stored in earthen pots.

Question 7.
Why do clothes dry faster on a sunny and windy day compared to rainy season ?
Answer:
If the amount of water vapour is high in air the rate of evaporation will decrease. So clothes dry slowly during rainy season but fast on a sunny and windy day.

Question 8.
Why do we require pressure cookers at higher altitudes?
Answer:
At higher altitudes the atmospheric pressure decreases. So the boiling point of water decreases. So, the heat energy supplied is not sufficient to cook food. Therefore we require a pressure cooker to increase the pressure. Thus the boiling point of water inside the cooker increases to 120°C and heat energy is sufficient to cook food.

Question 9.
Two pieces of cotton rolls one is soaked in ‘A’ chemical, and other one is soaked in ‘B’ chemical are inserted in a glass tube as shown in the figure.

a) If ‘A’ is HCl, what would be ‘B’?
b) In which state the rate of diffusion is high?
Answer:
a) If ‘A’ is HCl, then ‘B’ should be Ammonium solution. Because it formed Ammonium chloride.
b) Rate of diffusion is high to ‘B’ than ‘A’.
Because the product Ammonium chloride formed nearer to ‘A’ chemical.

Question 10.
One part of the substance was boiled in water at 100°C. Other part of the substance was boiled in water vapour at 100°C.
a) Which one would be boiled fast?
b) Guess the reason.
Answer:
a) Substance boiled in water vapour at 100°C is boiled fast.
b) Particles in water vapour at 100°C have more energy than the particles in liquid water at the same temperature. This is because of particles in water vapour have absorbed additional energy in the form of heat of vaporization.

Question 11.
Balaraju hanged his washed clothes under fan which is rotating.
Venu Gopal hanged his washed clothes under shadow.
a) Which one dries early? Why?
b) Write the name of the process that involved in drying.
Answer:
a) The clothes hanged by the Balaraju were dried faster, because, evaporation increases with wind speed.
Due to increase of wind speed, water vapour particles move away with the wind, decreasing the amount of water vapour in the surroundings.
b) The process involved in drying up the clothes is evaporation.

Question 12.
Observe the given graph and answer the following :

1. What is the melting point in the graph?
2. What is the boiling point in the graph?
3. Guess the substance.
4. What is the maximum temperature that hold the substance?

Answer:

1. The melting point is 0°C.
2. The boiling point is 100°C.
3. The substance should be water.
4. We can rise the temperature of the substance upto 100°C.
   The maximum temperature that hold by the water is 100°C.

8th Class Physical Science 3rd Lesson Matter Around Us 4 Marks Important Questions and Answers

Question 1.
How can you prove that the solids have definite shape and a fixed volume ?
Answer:

1. Take two solid objects, say a pen and a book.
2. Put them in different containers.
3. We observe that there is no change in their shape or volume.
4. Drop a book on the floor.
5. If will not flow like a liquid, but remain rigid.
6. These activities prove that solids have definite shape and a fixed volume.

Question 2.
What are the general properties of matter ?
Answer:
The general properties of matter:

1. Matter is made up of tiny particles. Their size is beyond our imagination.
2. Matter exists in three states i.e. solid, liquid and gas.
3. There exists space between the particles of matter.
4. There exists some force of attraction between the particles of matter.
5. Matter can change its state from solid to liquid, liquid to gas and vice versa, by changing temperature and pressure.
6. Matter has the properties of compressibility and diffusion.
7. Particles of matter move continuously in liquids and gases.

Question 3.
Define: a) Latent heat b) Latent heat of fusion c) Latent heat of vaporisation.
Answer:
a) Latent heat: The amount of heat energy that is required to overcome the attraction
energy among the particles is given by the latent heat of the substance.
b) Latent heat of fusion: Latent heat of fusion is defined as the amount of heat energy required to change 1 kg of a solid, completely into liquid at atmospheric pressure at its melting point.
c) Latent heat of vaporisation : Latent heat of vaporisation is defined as the amount of heat energy required to change 1 / of a liquid, completely into vapour at atmospheric pressure at its boiling point.

Question 4.
How is marine life possible in extremely cold areas ?
Answer:

1. The volume of water between 0°C to 4°C shrinks.
2. Same amount of water in solid ice occupies more volume than liquid water.
3. So ice floats on water rather than shrinking.
4. In extremely cold weather, the water at the top becomes colder and colder, until it freezes.
5. While the ice floats on the top, the animals continue to live in the water below, which does not freeze and remains at 4°C.
6. The ice on the top of the pond insulates the water, below it as it stops the water from losing the heat to air.
7. This is very important for survival of marine life which lives in ponds in the colder areas.

Question 5.
How does diffusion helps to survive the animals and plants in daily life ?
Answer:

1. It is clear that solids and liquids diffuses into liquids and gases diffuses into gases.
2. Certain gases from atmosphere particularly oxygen and carbon dioxide diffuse and dissolve in water and support the survival of aquatic animals and plants.
3. Diffusion therefore is a very important process for living things.
4. During respiration oxygen diffuses from lungs into blood. Carbon dioxide diffuses from blood into lungs.

Question 6.
How do you appreciate the process of diffusion ?
Answer:

1. Diffusion is a very important process for living things.
2. Oxygen diffuses into air and available for every human beings and animals.
3. CO₂ diffuses into air and available to plants.
4. Oxygen and CO₂ diffuse and disolve in water and support the survival of aquatic animals and plants.
5. During respiration oxygen diffuses from lungs into blood.
6. Smell of flowers, scents diffuses and reaches to our nose to give happiness to us.
7. We can recognise leaking of L.P. Gas in our house by diffusion process.
8. Diffusion of sugar and salt, give taste to drinks.
9. In this way diffusion is useful in our daily life.
   So, I am appreciating the process of diffusion.

Question 7.
How do you appreciate the process of evaporation ?
Answer:

1. The process of change of a liquid into vapours at any temperature below its boiling point is called “evaporation”.
2. It is very useful in our daily life.
3. Drying of wet clothes in air is the result of evaporation.
4. Drying of sweat from the human body and giving cooling is also result of evaporation.
5. After washing the floors, dishes evaporation takes place and dries up.
6. Water cools when it store in matkas (earthen pots). Evaporation process involved in it.
7. Water evaporate from the sea and forms clouds to rain.
8. In this way evaporation process is helpful to us.
9. So, I am appreciating it.

Question 8.
Find out the process involved in given situations.

Answer:
a) evaporation
b) melting
c) evaporation
d) diffusion
e) diffusion
f) boiling
g) diffusion
h) evaporation

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 2 Friction

AP State Syllabus 8th Class Physical Science Important Questions 2nd Lesson Friction

8th Class Physical Science 2nd Lesson Friction 1 Mark Important Questions and Answers

Question 1.
What is frictional force?
Answer:
The force which opposes the relative motion of two surfaces of bodies which are in contact is called frictional force.

Question 2.
What is static friction?
Answer:
Static friction is the friction which comes into play when surfaces of objects are at rest relative to each other

Question 3.
What is sliding friction?
Answer:
Sliding friction is the friction which comes into play when the surface of one object moves relative to the surface of another object.

Question 4.
What is rolling friction?
Answer:
When one body rolls over the surface of the other body the friction offered is called rolling friction.

Question 5.
Write the order of friction.
Answer:
Static friction > Sliding friction > Rolling friction.

Question 6.
What are lubricants?
Answer:
The substances which reduce friction are called lubricants.

Question 7.
What are the factors which influence friction?
Answer:
The factors which influence friction are: 1) Nature of surface, 2) Normal force.

Question 8.
What is drag?
Answer:
The frictional force exerted by fluids is called drag.

Question 9.
What are the factors which frictional force of an object in fluid depends on?
Answer:
The frictional force of an object in a fluid depepds on its speed with respect to fluid and on the shape of the object and nature of the fluid.

Question 10.
If friction was absent can you light a match stick?
Answer:
No, to light a match stick it is to be rubbed against the rough surface of a match box.

Question 11.
Hard metal balls are used between rolling parts in a machine. How does it reduces friction?
Answer:
Firstly it reduces the area of contact and reduces the friction. Secondly the hard balls experiences small forces of deformation that also reduce friction.

Question 12.
When a car is speeding on a level track, it enters on a concrete road from a tar road. What happens to its speed when the acceleration is unchanged?
Answer:
The friction between the tyres and the concrete road is less than that on the tar road. Therefore, the car accelerates more on the concrete road.

Question 13.
A car moving on a concrete road entered on a glacier. The driver applied brakes. Describe its motion.
Answer:
Because the friction is almost zero on the glacier, the car would not stop even though the tyres stop moving. That is the car skid forward.

Question 14.
Why do we use grease between moving parts of motor vehicles?
Answer:
To reduce friction and increase the efficiency of motor vehicles.

Question 15.
What is effect of roughness on friction?
Answer:
As the roughness of surface increases frictional force increases.

Question 16.
Why do Gymnasts apply some coarse substance on their hands?
Answer:
Gymnasts apply some coarse substance on their hands to increase friction for better grip.

Question 17.
What is the effect of area of contact on frictional force?
Answer:
Frictional force is independent of area of contact.

Question 18.
Why do we need to change the tyres when its threading is worn out?
Answer:
If we does not change the tyre then the frictional force decreases due to threading worn out tyre there by the vehicle may skid.

Question 19.
Why birds and fishes have special shapes?
Answer:
Birds and fishes have to move about in fluids all the time so they have special shapes which would make them not to lose much energy in overcoming friction.

Question 20.
Why shape of aeroplane is similar to bird?
Answer:
The shape of birds are useful in reducing the fluid friction so aeroplane shape was made similar to bird in order to reduce fluid friction.

Question 21.
How does life history of Leonardo Davinci inspire students?
Answer:
Leonardo Davinci was concerned with laws of science and nature which greatly informed his work as a painter, sculptor, inventor and draft men. His versatile personality inspire students.

8th Class Physical Science 2nd Lesson Friction 2 Marks Important Questions and Answers

Question 1.
What is practical application of static friction?
Answer:

1. The objects unable to move on their own is due to static friction otherwise no object be stationary at a particular place.
2. All the objects we used in our daily life are stationary because they unable to over-come static friction.

Question 2.
Why frictional force increases with roughness?
Answer:

1. Friction caused by the irregularities on the two surfaces which are in contact.
2. Irregularities on the two surfaces lock into one another and we have to apply force to overcome interlocking to move any surface.
3. On roughness surfaces there exists a large number of irregularities so the force of friction is greater if a rough surface is involved.

Question 3.
Give few examples for Sliding friction.
Answer:

1. The trolley moves on the floor.
2. The marbles or any spherical objects slide on the ground or floor when thrown.
3. The tyres make sliding movement on roads which moves the vehicles.

Question 4.
What happens if we do not reduce friction in machines?
Answer:
If we do not reduce friction in machines, then friction causes overheating and wearing out of moving parts of machinery.

Question 5.
What purposes are surved by using bearings in machines? Explain with daily life examples.
Answer:
Ball bearings are used to reduce friction between rotating shafts of machine tools.

1. Ball bearings are used in fAnswer:
2. Ball bearings are also used in machines.

Question 6.
Give examples of practical application of static friction.
Answer:

1. The static friction does not make the bodies move easily. So, the bodies are at rest.
2. The static friction helps the vehicles to come to rest.
3. The static friction helps us to escape from slippery.

Question 7.
Why does friction between two surfaces increase when they are pressed harder?
Answer:
Since the friction is due to the interlocking of irregularities in the two surfaces which slide with respect to each other, it is obvious that the force of friction will increase if the two surfaces are pressed harder.

Question 8.
Describe some examples where heat is produced due to friction.
Answer:

1. When we rub our hands together vigorously for few minutes we feel heat due to friction.
2. When we strike a matchstick, against rough surface, it catches fire due to friction.

Question 9.
Why are the soles of our shoes and tyres of cars, trucks, etc. grooved?
Answer:

1. It is done to provide the shoes better grip on the floor, so that one can move safely.
2. Similarly, the threaded tyres of cars, trucks and buldozers provide better grip with the ground.

Question 10.
Why heavier box apply more frictional force than lighter box?
Answer:

1. We know that the force of friction is increased if the two surfaces are pressed harder.
2. A heavier box presses the ground harder to heavier box apply more frictional force.

Question 11.
Why it is easy to move an object in motion when compared with object at rest?
Answer:

1. When the box start moving, the contact points on its surface, do not get enough time to lock into the contact points of floor.
2. So it is easy to move the box which already started to move.

Question 12.
What is the function of ridges on your palm and bottom of your feet?
Answer:
Ridges of our palm help us to make firm grip whenever we hold by our hands – Ridges of the bottom of our feet help us to walk freely and we do not slip because of these.

Question 13.
On what factors does the fluid friction depend?
Answer:

1. The frictional force on an object in a fluid depends on its speed with respect to the fluid.
2. The frictional force also depends on the shape of the object and the nature of the fluid.

Question 14.
Describe some examples where we have to increase friction.
Answer:

1. We will increase friction by using brake pads in the brake system of bicycles and automobiles.
2. Kabaddi players rub their hands with the soil for an easy grip of their opponents.
3. Gymnasts apply some coarse substances on their hands to increase friction for better grip.

Question 15.
Why is it easy to drag a mat over the floor when no weight is kept over it?
Answer:

1. When weight is kept over the mat, more force will be applied.
2. Due to more force, interlocking of two surfaces will increase, so friction also increases.
3. That is why it is easy to drag a mat over the floor when no weight is kept over it.

Question 16.
Explain why we use ball bearings between the hub and axle of ceiling fan and bicycle?
Answer:

1. Since the rolling friction is smaller than the sliding friction.
2. So sliding is replaced in most machines by rolling with the use of ball bearings.
3. Common examples are the use of ball bearings between the hub and axle of a ceiling fan and the bicycle.

Question 17.
Explain why Gymnasts apply some coarse substance on their hands?
Answer:

1. Gymnasts apply some coarse substance on their hands to increase friction for better grip.
2. This is due to increasing the large number of irregularities (up & downs) in the contact area.

8th Class Physical Science 2nd Lesson Friction 4 Marks Important Questions and Answers

Question 1.
What are the forces acting on a moving body on a floor?
Along vertical direction: Weight of the body (W) or gravitational force acting vertically down.

Normal force (N) or reaction force applied by the floor vertically up.
As there is no change in the motion of the body f along vertical direction the net force along vertical direction is 0.
That is W – N = 0 ⇒ W = N
Along horizontal direction : In horizontal direction the speed of the body changing gradually due to force, applied by the floor on the body. The force applied by the floor on the body is called frictional force.

Question 2.
What kinds of friction do you know and explain with suitable example.
Friction is of four kinds. They are:

1. Static friction: Friction which comes into play when surfaces of the objects are at rest relative to each other.
   Ex: 1) We are applying force on a big rock but unable to move the rock due to its static friction.
   2) Block at rest relative to the surface of trolley upto a certain limiting acceleration.
2. Sliding friction : The friction which comes into play when the surface of one object moves relative to the surface of another object.
   Ex: When the applied force is more than limit of static friction, then the object starts to move which is example for sliding friction.
3. Rolling friction : When one body rolls over the surface of another body, the friction offered is called rolling friction.
   Ex: It is easy to pull a suitcase which has rollers.
4. Fluid friction : Friction exerted by fluids like liquids and gases is called fluid friction. Ex : The shape of birds are such that they overcome the fluid friction.

Question 3.
A book placed on the surface of a table. The book is pushed in one direction. Draw the forces acting on the book and explain.
Answer:
The weight acts downwards and normal force acts upward direction they balance each other.

Whereas frictional force acting opposite to the applied force.

Question 4.
Explain with one example that Frictional force is proportional to the Normal force.
Answer:
Keep a brick on the horizontal floor tied to the spring balance. Pull the spring balance and note the frictional force.
Do the same experiment by adding one more brick above the first one.
Tie a brick to the spring balance and pull it to find the frictional force. The normal force acts on it provides a frictional force.

When we pull a brick over another brick the normal force acting on them increases so that the frictional force increases.
∴ Friction °c Normal force

Question 5.
Scientists designed the shape of aeroplane using the technique of reducing fluid friction by observing birds shape. How would you appreciate?
Answer:

1. Objects move through fluids, they have to overcome friction acting on them.
2. Birds and fishes have to move about in fluids all the time.
3. Their bodies must have evolved to shapes which would make them not to lose much energy in overcoming friction.
4. So aeroplanes designed in a special shape to overcome friction without loosing much energy.
   Hence I appreciate the idea of scientists to overcome fluid friction by designing shape of aeroplane.

Question 6.
Conduct an experiment to findout the effect of roughness on frictional force.
Answer:
Effect of roughness on frictional force:

1. Set up an inclined plane on the horizontal floor. Use a wooden board as inclined plane.
2. Put a mark at any point A on the inclined plane. Now let a pencil cell or ball move down from this point.
3. Note the distance covered by the pencil cell from the bottom of the inclined plane to point where it comes to stop.
4. Now, spread a cloth over the floor make sure that there are no wrinkles in the cloth.
5. Try again with pencil cell. Now note down the distance.
6. Distance covered by pencil cell is less in this case.
7. Thus we conclude that smoothness/ roughness of the surfaces of both the floor and the pencil cell could affect the distance travelled by it.

Question 7.
Collect information about the substances using to reduce the friction in different machines and prepare a report on it.
Answer:

1. Adding lubricants to machinery parts.
2. Using roller type ball bearings.
3. Using air pressure to separate moving parts.
4. Using magnetic repulsion to separate moving parts.
5. Using materials that tend to slide easily over each other.
6. Regulate the temperature of the machine.
7. The use of drive shafts.

Question 8.
Write an experiment to identify forces acting on a body and effect of frictional force.
Answer:
Gently push a book or any object on a horizontal floor. It moves for a certain distance and stops due to the friction.
The friction acts in the opposite direction of the force exerted.
Now take the same object and do the activity on different surfaces smooth and rough.
The object moves a long distance on the smooth surface whereas it moves a little distance on the rough surface.
We come across that the friction is more on the rough surface and less on the smooth surface due to the reduction in the sliding friction.

Question 9.
Friction – an evil master and good servant to man. Describe.
Answer:
Friction is the obstruction force acting in the opposite direction of the exerted force. It brings the following bad or evil impacts on the bodies.

1. Over heating and wearing out of moving parts in all machinery
2. Loss of efforts

In this way it is a bad or evil master to man.
But, without friction the moving of vehicles on the roads, walking, running, sitting, standing, etc. of us are not possible.
We are able to write with pen or pencil on the papers or walls or any surface is only due to the influence of friction. .
In this way it is a good master.

Question 10.
Does the friction is affected by smoothness of surface? Explain.
Answer:

1. Friction is caused by the irregularities on the two surfaces in contact.
2. Even those surface which appear very smooth have a large number of minute irregularities on them.
3.  Irregularities on the two surfaces lock into another.
4. When we attempt to move any one surface over the other, we have to apply a force to overcome interlocking.
5. On rough surfaces, there are a larger number of irregularities.
6. So the force of friction is greater if a rough surface is involved.

Question 11.
What would happen if there were no force of friction? Imagine and describe in your own words.
Answer:

1. If there were no friction, many problems could have been arisen, as one will not able to walk if they were no friction at all.
2. One could not write with pen or pencil.
3. One could not write on blackboard with a chalk.
4. If any object just started moving, it would never stop.
5. Had there been no friction between the tyres of the automobiles and the road, they could not be started or stopped or turned to change the direction of motion.
6. One could not fix the nail in the wall or tie a knot.
7. Without friction no buildings could be constructed.

8th Class Physical Science 2nd Lesson Friction Important Questions and Answers

Question 1.
“Friction produce heat” – suggest an activity to prove this.
Answer:

1. Rub your palms against each other for a few minutes.
2. You can feel heat in your palms.
3. Hence we can say that friction produces heat.

Question 2.
Write any one precaution which was taken by you while doing the experiment to understand the nature of friction.
Answer:
Keep the weights to the hanger slowly and one by one.

Question 3.
Give any two examples of ways of reducing friction.
Answer:
We can reduce friction,

1. by using lubricants in between frictional surfaces,
2. by using ball bearings in the rotating parts.

Question 4.
If there is no frictional force, assume the consequences in your classroom. Write any four of them.
Answer:
If there is no friction force,

1. We cannot hold a pen to write on a book.
2. We cannot walk in the classroom.
3. Teacher cannot write with chalk-piece on the blackboard.
4. Heat does not produce when rub the palms against each other.

Question 2.
What is fluid friction? Explain why objects moving in fluids must have special shapes.
Answer:

1. When bodies move through fluids, fluids exert a frictional force called drag or fluid friction.
2. To minimise fluid friction, objects moving in fluids must have special shapes.
3. For example, Birds and Fishes have to move about in fluids all the time, so they have special shapes which would make them not to lose much energy in over coming friction.
4. Another example is the shape of aeroplane was made similar to bird in order to reduce fluid friction.

Question 3.
Imagine the friction has disappeared from the earth. What will happen? Explain.
Answer:

1. If there were no friction, many problems could have been arisen, as one will not able to walk if they were no friction at all.
2. One could not write with pen or pencil.
3. One could not write on blackboard with a chalk.
4. If any object just started moving, it would never stop.
5. Had there been no friction between the tyres of the automobiles and the road, they could not be started or stopped or turned to change the direction of motion.
6. One could not fix the nail in the wall or tie a knot.
7. Without friction no buildings could be constructed.

Question 4.
Name any two types of frictions. Write one example for each.
(OR)
What kinds of friction do you know? Write the conditions needed for static friction between two objects and what way do you suggest to reduce friction?
Answer:
Friction is of four kinds. They are

1. Static friction: Friction which comes into play when surfaces of the objects are at rest relative to each other.
   Ex : 1) We are applying force on a big rock but unable to move the rock due to its static friction.
   2) Block at rest relative to the surface of trolley upto a certain limiting acceleration.
2. Sliding friction: The friction which comes into play when the surface of one object moves relative to the surface of another object.
   Ex : When the applied force is more than limit of static friction, then the object starts to move which is example for sliding friction.
3. Rolling friction: When one body rolls over the surface of another body, the friction offered is called rolling friction.
   Ex : It is easy to pull a suitcase which has rollers.
4. Fluid friction: Friction exerted by fluids like liquids and gases is called fluid friction. Ex : The shape of birds are such that they over come the fluid friction.

Static friction is a self adjusting force. The following conditions are needed for static friction ;

1. Roughness of the surface of contact and
2. Normal force.
3. We can reduce the friction by applying oil or grease between the moving parts of a machine.
4. If we polish the rough surfaces, they become smooth and friction is reduced.
5. We can apply soap solution to the rough surfaces.
6. We can apply powder of small quantity on the surface.
7. By streamlining the bodies of the vehicles we can reduce air friction.

Question 5.
Friction does not depends upon area of contact. How can you perform an activity to prove it?
Answer:
Tie a string around a brick and pull the brick by using spring balance and measure the applied force or friction.

Now turn the brick upright so that the contact area with the floor becomes small. Do the same experiment and measure the friction using the reading of the spring balance.

The conclusion is frictional force appears the same in both the cases irrespective of area of contact.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 1 Force

AP State Syllabus 8th Class Physical Science Important Questions 1st Lesson Force

8th Class Physical Science 1st Lesson Force 1 Mark Important Questions and Answers

Question 1.
What is force ? What is its S.I. unit?
Answer:
The push or pull of an object is called force. Its S.I. unit is Newton.

Question 2.
What is a contacting force?
Answer:
The force results when there is a direct physical contact between two interacting objects is called contacting force.

Question 3.
Define a force at a distance or field force.
Answer:
The force which occurs without any physical contact between two objects is known as force at a distance or field force.

Question 4.
What is muscular force?
Answer:
The force which we exert by using our body muscles is known as muscular force.

Question 5.
What is friction?
Answer:
The resistance to the movement of a body over the surface of another body is called friction.

Question 6.
Define normal force.
Answer:
The force that a solid surface exerts on any object in the normal direction is called normal force.

Question 7.
What is a magnetic force?
Answer:
The force exerted by a magnet on another magnet.

Question 8.
What is a gravitational force?
Answer:
The attractive forces between any two massive objects is called gravitational force.

Question 9.
What is electrostatic force?
Answer:
The force exerted by a charged body on other charged or uncharged body is called electrostatic force.

Question 10.
What is magnetic field?
Answer:
The space around the magnet where its influence can be detected is called magnetic field.

Question 11.
What is a net force?
Answer:
The algebraic sum of the forces acting on a body is known as net force.

Question 12.
What is free body diagram?
Answer:
The diagram showing all the forces acting on an object at a particular instant is called free body diagram.

Question 13.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
It changes the shape of iron.

Question 14.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad?
Answer:

1. The weight of the rocket downwards.
2. The upward force due to firing of rocket.

Question 15.
Why do not you experience gravitational force exists between you and your teacher because gravitational force depends on masses of object
Answer:
The reason is everything on earth experienced by a large gravitational force of earth so remaining gravitational forces are negligible.

Question 16.
What is tension?
Answer:
When we stretch a rope or a string the tightness of rope or string is called tension. Tension is a contact force.

8th Class Physical Science 1st Lesson Force 2 Marks Important Questions and Answers

Question 1.
Explain Gravitational Force by giving a suitable example.
Answer:
Gravitational Force: The force of attraction that exists between any two bodies (or masses) everywhere in the universe.
Examples:

1. The stone thrown up into the sky fall back on to the earth due to gravitational force.
2. Earth holding atmosphere due to gravitational force.
3. All the objects are pulling towards earth due to gravitational force.
4. Rivers flow down to the sea because of gravitational force.

Question 2.
The surface area of an object is 20 m² and a force of 10 N is applied on it, then what is the pressure?
Answer:
Force (F) = 10 N; Area (A) = 20 m × 2m = 40m²;
Pressure = \(\frac{F}{A}\) = \(\frac{10}{40}\) = 0.25 Pascal

Question 3.
Observe the situations of electrostatic forces in your daily life and prepare a report.
Answer:

1. If you comb your dry hair and bring small pieces of paper then these paper pieces are attracted by comb because it is charged.
2. If a glass rod is rubbed with a silk cloth then if we bring small pieces of paper near glass rod or silk cloth then these paper pieces are attracted by glass rod or silk cloth due to elctrostatic force.

Question 4.
Find the net force acting on a body shown in the figure. And draw the direction of net force. (Length of the arrow shows the magnitude of the force and direction also.)
Answer:

Question 5.
Give two daily life examples each of situations in which you push or pull to change the state of motion of object.
Answer:
Push:

1. Hitting a foot ball with your leg.
2. Moving a loaded cart.

Pull:

1. Opening a door
2. Moving a table towards you.

Question 6.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:

1. Pressing a sponge.
2. Stretching of rubber band.

Question 7.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Why do the forces acting on the bucket do not bring a change in its state of motion?
Answer:
The gravitational force acts as plastic bucket containing water held above ground level in your hand. Gravitational force does not bring change in state of bucket be¬cause equal amount of force is applied vertically upward.

Question 8.
Name the two forces acting on a rocket immediately after leaving the launching pad.
Answer:
The two forces acting on rocket are:

1. Force due to gravity vertically downward.
2. Frictional force of atmosphere.

Question 9.
What changes can be observed when we apply force on an object?
Answer:
a) Change in the shape of the object.
b) Change in direction of motion of an object.
c) Change in speed of an object if the object is moving.
d) Movement of an object from rest.

Question 10.
Have you ever seen a game of tug of war ? In this game two teams pull a rope in opposite direction. But sometimes the rope does not move explain why.
Answer:
a) When two forces acts on an object in opposite direction then the net force is difference of two forces.
b) If two teams pull the rope with equal force, the forces will be in opposite direction and will cancel with each other and the rope will not move.

Question 11.
How does an applied force change the speed of an object ?
Answer:

1. When force is applied in the direction of motion of object then the speed of object increases.
2. If the force is applied in the direction opposition to the motion of object then the speed decreases.

Question 12.
Give three examples of force exerted by muscles in our body.
Answer:

1. Blood circulation in our body.
2. Inhalation and exhalation of air by lungs.
3. Running by muscles of legs.

Question 13.
Why does the pointed end of the nail gets into wooden plank easily ?
Answer:
The area of pointed end of nail is much smaller than that of its head. The same force produces a sufficient pressure to push the printed end of the nail into the wooden plank.

Question 14.
Why do porters place a round piece of cloth on their heads?
Answer:
Porter place a round piece of cloth on their heads to increase the area of contact of the load with the head. So the pressure on their head is reduced and they can carry heavy load easily. .

Question 15.
On what factors does the effect of force depend?
Answer:
The effect of force depends on two things

1. The amount of force applied the more the force applied the greater the effect will be.
2. The area on which the force is applied. The smaller the area, the force is applied on the greater the effect will be.

Question 16.
How many types of forces are there and what are they? Give examples for each.
Answer:
Forces are two types:

1. Contact force e.g.: Muscular force, frictional force.
2. Force at a distance e.g.: Gravitational force, magnetic force.

Question 17.
What is pressure ? What is its unit?
Answer:
The force acting perpendicularly on a unit area of surface is called pressure.
Pressure = Force/Area
Its unit in S.I. system is Newton / metre or N/m .

Question 18.
What is the influence of Sir Isaac Newton on students?
Answer:

1. Everything we are discussing about motion and his contribution to mechanics and light one of the all time greatest scientist.
2. His experiments and laws, hypothesis influence the students to take up research and inspire them to become a future scientists of our nation.

8th Class Physical Science 1st Lesson Force 4 Marks Important Questions and Answers

Question 1.
Design and conduct experiment to test few ways how friction may be reduced.
Answer:
Friction is due to the roughness of surfaces. It can be reduced by the following methods.

1. By polishing the rough surface.
2. By applying lubricants like oil and grease to the surfaces.
3. By spreading powder on the rough surface like carromboard.
4. By using soap and detergent solutions, etc.

Experiment: The rusted pulley makes a rattling noise. Apply some oil in between the wheel and axle. The sound is reduced and now it works smoothly.

Question 2.
Collect pictures to illustrate contact forces, forces at a distance and prepare a report.
Answer:
I. Contact forces :
1) Muscular force:

2) Frictional force:

3) Normal force:

4) Tension:

II. Forces at distance (Field Forces)
1) Magnetic force:

2) Electrostatic force:

3) Gravitational force:

Report: Forces are two types based on contact or non-contact between objects.

I. Contact Forces : Force which results when there is a direct physical contact between two interacting objects is known as contact force. Contact forces are four types. They are :

1. Muscular Force: The force which we exert by using our body muscles is known as muscular force.
2. Frictional Force: Friction is the resistance to the movement of a body over the surface of another body.
3. Normal Force: The force that a solid surface exerts on any object in the normal direction is called normal force.
4. Tension: The lightness of slope or string when we try to stretch a rope or string is called tension.

II. Forces at distance (Field forces): The force which occurs without any physical con¬tact between two objects is known as a force at distance or field force.
Forces at distance are three types. They are:

1. Magnetic Force : The force existing between two magnetic poles of two different magnets is called magnetic force. The force is also exists between magnet and magnetic material.
2. Electrostatic Force : The force exerted by a charged body on another charged body is known as electrostatic force.
3. Gravitational Force : The force of attraction exists between any two bodies (or masses) everywhere in the universe is known as gravitational force.

Question 3.
When you push a heavy object, it doesn’t move. Explain the reason in terms of net force.
Answer:
There are four forces acting on the heavy table. They are normal force (upwards), gravitational force (downwards), push and friction (opposite to push).

Let’s take
Normal force = N (- ve); Gravitational Force = W (downwards); Push = F₁
Friction = F₂ (- ve) [more]
∴ Net force in X – direction = Push – Friction = F₁ – F₂ = – ve
Net force in Y – direction = N – W = – ve
As the net force in Y – axis is more you are unable to move the heavy object.

Question 4.
Some forces are acting without any contact of surfaces. Explain.
Answer:
Some forces like magnetic force, electrostatic force and gravitational force act on other bodies without any contact of surfaces. This property is called the field force.
As far as magnetic force concern, the magnets are surrounded by the magnetic lines of force which provide the magnets attractive and repelling forces. The same poles repel and the different poles attract.
The electrostatic forces are exerted by a charged body on another charged or uncharged body. The charged body induces an opposite charge on the uncharged body and it gets attracted by the body. Here, the two bodies are at distance before the electrostatic forces are exerted.
The earth attracts everybody even though they are at some distance. This force is called gravitational force or weight of the body. It varies at different places.

Question 5.
In the following situations identify the agent exerting the force and the object on which its acts. State the effect of force in each case.
a) A batsman hitting a cricket ball
b) Pressing a lump of dough
c) Taking out paste from a tooth paste
d) A horse pulling a cart
Answer:

Agent exerting force	Object on which it acts	Form of effect
Muscles	Cricket ball	Change in speed and direction
Fingers	Dough	Change in shape
Fingers	Tooth paste	Change in shape
Horse	Cart	Change in speed

8th Class Physical Science 1st Lesson Force Important Questions and Answers

Question 1.
A fruit is falling from a tree. Which force acts on the fruit?
Answer:
Gravitational force acts on the fruit, which is from a tree.

Question 2.
Find the net force from the following diagrams.

Answer:
a) Net force = + 12N + 10N – 8N = + 22N – 8N = 14 N
b) Net force = +9N – 8N = 1N

Question 3.
If you bring a rubbed balloon near the pieces of paper, what do you observe ?
Answer:
Rubber balloon attracts pieces of paper. It is electrostatic force.

Question 4.
From the above diagram, calculate the net force acting on a body.

Answer:
Net force in vertical direction = 5N – 5N = 0
Net force in horizontal direction = 10N – 8N = 2N

Question 5.
Find the net forces from the following free body diagram (FED).

Answer:
i) Net force in the vertical direction = + 6N – 6N = 0N
ii) Net force in the horizontal direction = + 20N – 3N = 17N.

Question 6.
What will happen if gravitational force disappears from the Earth? Explain.
Answer:
If gravitational force disappears from the earth,
i) No atmospheric gases are found around the earth.
ii) Objects does not fall down on the earth.
iii) Human beings, animals can fly easily in the sky.
iv) We cannot find the weight of the objects.

Question 7.
Define contact force and force at a distance, give two examples for each type of force.
Answer:
Contact force: The force results when there is a direct physical contact between two interacting objects is called contacting force.
Example: Muscular force, Frictional force, Normal force, Tension.
Field force or Force at a distance : The force which occurs without any physical contact between two objects is known as force at a distance or field force.
Example : Magnetic force, Electrostatic force, Gravitational force.

Question 8.
Using adjacent diagram, draw a free body diagram (FBD) to show the forces acting on the box.

Answer:

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 11 Some Natural Phenomena Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 11th Lesson Some Natural Phenomena

8th Class Physical Science 11th Lesson Some Natural Phenomena Textbook Questions and Answers

Improve Your Learning

Question 1.
Which of the following cannot be charged easily by friction?
A) A Plastic scale
B) A copper rod
C) An inflated balloon
D) A Woollen cloth
E) Piece of wood
Answer:
(B) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
A) and the cloth both acquire positive charge.
B) becomes positively charged while cloth has a negative charge.
C) and the cloth both acquire negative charge.
D) becomes negatively charged while cloth has a positive charge.
Answer:
(B) becomes positively charged while cloth has a negative charge.

Question 3.
Identify ‘True’ or ‘False’ sentences among the following:
A) Like charges attract each other. (T/F)
B) A charged glass rod attract a charged plastic straw. (T/F)
C) Lightning conductor cannot protect a building from lightning. (T/F)
D) Earthquakes can be predicted in advance. (T/F)
Answer:
A) False
B) True
C) False
D) False

Question 4.
Sometimes, a crackling sound is heard while taking off sweater during winter. Explain.
Answer:
Charge is developed on the sweater because of friction. We can observe discharge of the charge while taking off the sweater which produce the crackling sound.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
The reason is that the charged object lose charge to the earth through our body that means it is transferred its charge to earth. The process of transferring of charge from a charged object to the earth is called earthing.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
The destructive energy of earthquake is measured in richter scale. Yes, it would be recorded by seismograph when earthquake measures 3 on the richter scale. It does not cause any damage to human life, generally we unable to felt its effect.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
Precautions to be taken to protect ourselves from lightning.

1. Staying in a house or building of low height.
2. If we are travelling in a bus or car, then we are safe inside the car or bus provided doors and windows are closed.
3. If we are in a forest taking shelter under shorter trees than taller trees is a good idea during the thunder storm.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by a charged balloon?
Answer:
A charged balloon is repelled by another charged balloon having same type of charge because both are having same kind of charges and like charges repel each other. Whereas an uncharged balloon attracted by a charged balloon because charged balloon induces opposite charge on uncharged balloon. We already know unlike charges attract each other. So the uncharged balloon is attracted by a charged balloon.

Question 9.
List three states in India where earthquakes are more likely to occur?
Answer:
The three states are

1. Jammu & Kashmir State (Mainly Kashmir)
2. Whole north east states like Tripura, Manipur, etc.
3. Rajasthan.

Question 10.
Does your habitation lie in earthquake prone area? Explain.
Answer:
Yes, my habitation lie in earthquake prone area because 1 am living in delta region of Krishna which is placed in seismic zone III. So it has chances of possibility of earthquake. (If the answering person is not living in Chittoor, YSR Kadapa, Nellore districts and Krishna and Godavari delta region then the answer is No.)

Question 11.
Which place in Andhra Pradesh experiences earthquakes most of the time?
Answer:
Badrachalam and Kothagudem are the places where there is a possibility of earthquake most of the time. Chittoor, Kadapa, Nellore and Krishna and Godavari delta region also have greater possibility of earthquake because they lie in zone-111.

Question 12.
When does a piece of matter have a “charge?”
Answer:
When a piece of matter rubbed with another piece of matter, the piece of matter acquire charge due to friction.
E.g.: Rub the refill vigorously with a piece of polythene and if we bring piece of paper that can be attracted by refill due to development of charge.

Question 13.
What happens if two objects having same charge brought close to each other? What happens if two objects having different charges are brought close? Can you give an example for this.
Answer:
Two objects having same charge repel each other and two objects having different charge attract each other.
E.g. A balloon rubbed with woollen cloth repelled by another balloon rubbed with woollen cloth because both will acquire same type of charge.
A balloon rubbed with a woollen cloth attracted by a refill rubbed with a polythene sheet because both will acquire different type of charge.

Question 14.
Give two examples of effects in your daily life caused by transfer of charges.
Answer:
Two examples in daily life:

1. Earthing
2. Lightning

Question 15.
Inflate two balloons and rub both of them with a cloth first and then with different material. Will they attract each other in both cases?
Answer:
No, they will not attract each other. Both will repel each other. The reason is both ballons rubbed with same material acquired same charge in the both the cases.

Question 16.
Which country in the world is frequently affected by earthquakes? Collect the information and photographs on the recent earthquake in Japan.
Answer:
The country in the world which frequently affected by earthquakes is Japan. Pictures of earthquake affected areas in Japan in 2012.
Photographs of earthquake:

Information about earthquake:

1. Lot of people killed due to earthquake.
2. Lot of people killed not only due to earthquake but tsunami caused by earthquake.
3. Lot of property loss took place.
4. Most of the people in Japan lost their jobs and livinghood.
5. They suffered emotionally also by losing their relatives, parents and children.
6. Lot of effect felt on their economy.
7. It effected the tourism of Japan.

Question 17.
Find out if there is an organization in your area which provides relief to those suffering from natural disaster. Enquire about the type of help they render to the victims of earthquake. Prepare a brief report on the problems of the earthquake victims.
Answer:
In India National Disaster Force provides relief for disaster victims.
Problems of earthquake victims:

1. Death: Many times, the people who support a family socially and economically dies. This causes most of the other members of the family to either fight their way through, or restart their lives from the bottom of the food chain.
2. Destroyed Structures: If the members of the family survive, then they could still be short of a home. The earthquake would have caused the destruction of their house and because of that, they would be left homeless.
3. No food or water: In the aftermath of an earthquake, people see whether all the pipelines, roads, etc. are in good shape or order. If the pipes are broken, then water scarcity begins. If the roads are broken, then food supplies cannot be transported, later causing problems in food scarcity.
4. Electricity : With inadequate supply of electricity, the debris and rubble will take a lot of time and if people are under it then they may die before the rubble is removed.
5. Illnesses: After the destruction of many buildings, the sewer pipes will also break and open, causing spread of disease everywhere.

Help render by relief organisation:

1. They minimize the death of people.
2. They provide drinking water and food for victims.
3. They provide shelter for earthquake victims.
4. They provide medical facility for earthquake victims.

Question 18.
How do you relate the energy release during the collision of fault lines during earthquake to the atmospheric variation on the surface of the earth?
Answer:
An earthquake effects the atmosphere by creating amounts of debris and dust which will add to the air that we breathe. Earthquakes can also trigger volcanoes which will release tonnes of ashes and other debris into the atmosphere. This can sometime cause the blocking out of the sun, air pollution and are increased amount of carbon in the air.

Question 19.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
The instrument used to detect a charged body is electroscope.
Description of Electroscope:
Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it, so that a metal paper clip could be inserted. Open out paper clip as shown in the figure. Cut two strips of aluminium foil about 4 x 1 cm each and hang them on the paper clip.

Insert the paper clip having the strips of aluminium foil into the cardboard lid so that it is perpendicular to it. This entire device works as a electroscope.
Procedure to detect a charged body ,by using a electroscope:
Charge a refill and make it touch the end of the paper clip. The aluminium foils move away from each other the reason that the strips of aluminium foil receive the same charge from the charged body through the paper clip and strips carrying similar charges repel each other and hence they move apart. This proves electroscope is useful in detecting a charged body.

Question 20.
Colour seismic zones in India out line map.
Answer:

Question 21.
Prepare a model of seismograph.
Answer:
Preparation of model:

Take a pendulum and which is attached to support. This acts as vibrating system. A pen is attached to this vibrating system. Place a rotating drum covered with a paper just below the pen. When earthquake occurs the pen records the seismic waves on a paper which move under it.

Question 22.
How do you appreciate the efforts of scientists to develop an instrument to assess the intensity and source of earthquake?
Answer:
The efforts of scientists to develop an instrument to assess the intensity and source of earthquake is thoroughly appreciated because they provide assessment of earthquake and what are the rescue measurements to be taken by government and private organizations and also provide preventive measurements that would be taken when earthquake occurs. So these scientists providing life for people and their services are thoroughly appreciated.

Question 23.
Suppose you are outside your home and an earthquake occurs. What precautions would you take to protect yourself?
Answer:

1. I find a clear spot, away from buildings, trees and over head powerlines and I drop to the ground.
2. If I am in a car or bus, I do not come out and I ask the driver to drive slowly to a clear spot. I do not come out of the car or bus till the tremors stop.

Question 24.
The weather department has predicted that a thunder storm is likely to occur at on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, I would not carry umbrella during thunderstorm because the metallic rod attached to the umbrella attracts the charge developed in thunderstorm and charge may carry through umbrella and possibility of electric shock. So it is not a good idea to carry umbrella during lightning.

Question 25.
If earthquake occurs in your area what will you do?
Answer:

1. I will protect myself by covering head with helmet or cushion and hide in a safe place, such as under table.
2. I will not run outside because roof tiles and glass may fall on me.
3. Major after shocks can come after smallest earthquake so I calmly extinguish any nearby flames.
4. Earthquake can wrap buildings, especially apartment buildings making it impossible to open doors and escape. So I open doors and windows to secure an escape route.
5. I will be careful with broken glass.
6. Once I come outside I will not return to house.
7. I will avoid phone calls.

Question 26.
What are the measures you would take in your house when an earthquake occurs?
Answer:

1. I would take shelter under a table and stay there till the shaking stops.
2. I would stay away from tall and heavy objects that may fall on me.
3. If I would be in the bed then I would not get up and I protect my head with a pillow.

8th Class Physical Science 11th Lesson Some Natural Phenomena Activities

Activity – 1

Question 1.
Effect of rubbing:

Take a used ball-pen refill and bring it near small pieces of paper.
The refill should be close enough but not touch the pieces of paper.
a) Check what happens to the paper pieces?
Answer:
They remain in the same position.
Now, rub the refill vigorously with a piece of polythene. Bring it close to small pieces of paper.

b) What is your observation. Take care that the rubbed end is not touched by your hand or with a metallic object.
Answer:
My observation is paper piece is attracted towards refill.
Now, take a comb and move it through dry hair a few times. Take the comb near small pieces of paper and check what happen.
The papers are attracted by comb.
Take an inflated balloon and rub it against your clothes. Bring the balloon close to small pieces of paper.
The paper pieces are attracted by balloon.
Take a drinking straw and rub it against a smooth wall or against your cloths, then bring it near pieces of paper.

c) What do you observe?
Answer:
The papers are not attracted by drinking straw.

d) Are they able to attract bits of paper after being rubbed?
Answer:
No, they are not attract bits of paper.
Repeat the activity by rubbing each one of the above mentioned objects (refill, comb, drinking straw, balloon) and use small pieces of dry leaf, husk, etc. as testing materials. Record your observation in table.

e) What can we infer from the above activity?
Answer:
When you rub material some material tend to attract pieces of paper.

f) Do objects like refill or comb attract pieces or paper only after rubbing?
Answer:
Yes, they attract pieces of paper only after rubbing.

g) Do all objects show this property?
Answer:
No, all the objects does not show this property.

h) Can we rub a comb against our palm and make it attract the paper bits?
Answer:
Yes, the paper bits are attracted to the palm due to friction charge is developed on the hand.

Lab Activity

Conduct an experiment of find the effects of charged bodies which have been rubbed by different materials.
Aim: To find effects of charged bodies which have been rubbed by different materials.
Materials required: A ball pen refill, a balloon, a comb, an eraser, a steel spoon, polythene sheet, plain paper, woollen cloth, etc.
Procedure:
Rub the above objects against materials listed in table. In each case, bring the rubbed object near small pieces of paper and note whether they attract pieces of paper or not. Record your observations in table by writing ‘yes’ or ‘no’.

a) What do you conclude from above table?
Answer:
Some objects like refill, comb when rubbed with specific materials able to attract light objects like bits of paper. But some objects like steel spoon do not attract pieces of paper even after rubbing.

b) Why don’t some materials attract pieces of paper even after rubbing ?
Answer:
The reason is some material acquire charge when we rub them and some may not acquire charge so they do not attract pieces of paper.

Activity – 2

Question 2.
Understanding types of charges:
Inflate two balloons and hang them in such a way that they do not touch each other. Rub both the balloons with woollen cloth and release them.

a) What do you observe?
Answer:
They repel each other. Take a refill and rub it with a polythene sheet. Keep it gently in a plastic tumbler. Take another refill and also rub it with the same polythene sheet.
Bring the second refill near the first one in the tumbler. Take care that you do not touch either of the rubbed portions on the refill with your hand.

b) Is there any effect on the first refill in the tumbler? Do they attract each other or repel each other?
Answer:
Yes, there is effect on the refill in the tumbler. They repel each other.

c) Now take a rubbed balloon near the rubbed refill in the tumbler and check the action. Do they attract each other or repel each other.
Answer:
They attract each other.
In the first two parts of the above activity, two objects that were made of the same material have brought near to each other after being rubbed with some appropriate material.

In the third part, objects made of different materials were brought near to each other after being rubbed with some material.
Let us summarise our observations carefully.

1. A balloon rubbed with woollen cloth repelled another balloon of the same type.
2. A refill rubbed with polythene repelled another refill rubbed with similar material.
3. A ballon rubbed with woollen cloth attracted by a refill rubbed with polythene sheet.

d) What can we conclude from these observations?
Answer:
Some charged objects are attracted and some charged objects are repelled with each other.

e) Does the repulsion between charged balloons indicate that they possess similar charge?
Answer:
Yes, they possess similar charge.

f) Does the attraction between charged balloon and a charged refill indicate that they possess different charges?
Answer:
Yes, they possess different charges.

g) Does this activity remind you some of experiments that you have done in “Playing with Magnets” Chapter of class VI?
Answer:
Yes, we know that magnets attract objects made up of magnetic materials like iron, nickel, cobalt, etc.
We also know that unlike poles magnet attract each other and like poles repel each other.

h) Can we say that something similar is happening in above activities?
Answer:
Yes.

i) Does it indicate that the charge on the balloon is of a different kind from the charge on the refill?
Answer:
Yes, it indicate they are different charges.

j) Can we say that there exist two kinds of charges?
Answer:
Yes, there exists two kinds of charges.

k) Can we also say that the charges of same kind repel each other, while charges of different kinds attract each other?
Answer:
Yes, it is convention to call the charge acquired by a glass rod when it is rubbed with silk cloth positive and charge acquired by a silk cloth is negative.
It is observed that when a charged glass rod is brought near a charged plastic straw which is rubbed with polythene sheet, there is attraction between the two.

l) What do you think about the kind of charge on the plastic straw?
Answer:
The plastic straw would carry negative charge.

m) Is your guess correct or wrong? Discuss with your teacher.
Answer:
My guess is correct because opposite charges attract each other which I confirmed by discussing with my teacher.

Activity – 3

Question 3.
Conduct an experiment to find out the presence of charge on a body.
Make a small ball of thermocol. Collect thin silver foil used to decorate sweets.
Wrap this thin silver foil to cover the thermocol ball and suspend it from a stand with the help of thread as shown in figure.

Bring a glass rod which is rubbed with a silk cloth near the suspended ball.
a) What happens ? Does it get attracted towards the glass rod or move away from it?
Answer:
It will attracts towards glass rod.
Now touch the silver foil on the thermocol ball with charged glass rod. Remove the glass rod from the ball and against rub it with silk cloth and bring it close to the suspended ball.

b) What do you observe?
Answer:
The suspended ball moves away from the glass rod.

c) What could be the reason for this change in movement of the ball?
Answer:
In the above activity when a charged body brought near an uncharged body it induces an opposite charge in it and hence it get attracted by the glass rod.
In the second case we have charged the thermocol by touching it with a charged glass rod. Hence when we brought the glass rod near the ball, as both of them have similar charge the ball gets repelled by the glass rod.
From the above activity we can conclude that attraction is not a sure test to know the presence of charge on a body.

Activity – 4

Question 4.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle.
Pierce a hole in it so that a metal paper clip could be inserted.

Open out paper clip as shown in the figure.
Cut two strips of aluminium foil about 4 cm x 1 cm each and hang them on the paper clip.
Insert the paper clip having the strips of aluminium foil in to the cardboard lid so that it is perpendicular to it as shown in the figure.
Change a refill and make it touch the end of the paper clip. Observe what happens.
a) Is there any effect on the strips of aluminium foil?
Answer:
Yes.

b) Do they repel each other or attract each other?
Answer:
They repel each other.

c) Now bring other charged bodies and make them touch the end of the paper. Do the foil strips behave in the same way in all cases?
Answer:
Yes, it behave in the same way in all cases.

d) Can this apparatus be used to detect the presence of charge on a body or not?
Answer:
Yes, it is used to detect the presence of charge on a body.

e) Can you explain why the strips repel each other?
Answer:
The strips of aluminium foil receive the same charge from the charged refill through the paper clip. The strips carrying similar charges repel each other and hence they move apart.
This device can be used to test whether an object is carrying charge or not. This device is known as electroscope. In the above activity you can observe that electric charge can be transferred from a charged object to another through a metal conductor.
Touch the end of the paper clip gently with hand and you will find a change in the foil strips they move closer and come back to their original state.

f) Why does it happen?
Answer:
The reason is that the foil strip lose charge to the earth through your body. We say that the foil strips are discharged.
The process of transferring of charge from a charged object to the earth is called earthing.

Activity – 5

Question 5.
Collecting information about the damages caused by earthquakes:
Ask your parents about the huge damages to life and property caused by these earthquakes. Collect a few pictures showing the damage caused by these earthquakes from newspapers and magazines of those days.
Prepare a short report on the suffering of the people during the earthquakes.
Answer:
Report: It caused damage to human life and property on a hugescale. Due to tsunami thousands of people died in the coastal areas of Andhra Pradesh and Tamilnadu. People lost their shelter.
a) What is an earthquake?
Answer:
An earthquake is a sudden shaking or trembling of earth lasting for a very short period of time. It is caused by a disturbance deep inside the earth’s crust.

b) What happens when it occurs?
Answer:
When it occurs it can cause damage to human life and property on a huge scale.

c) What can we do to minimize its (earthquake) effects?
Answer:
People living in seismic zones, where the earthquakes are more likely to occur, have to be specially prepared. The buildings in these zones should be designed so that they can with stand major tremors.
Steps to be taken in building construction:

1. In highly seismic areas, the use of mud or timber is better than heavy construction material.
2. Keep roofs as hieght as possible. In case the structure falls, the damage will not be heavy.
3. It is better if the cupboards and shelves are fixed to the walls so that they do not fall easily.
4. Be careful where you hang wall clocks, photoframes, water heaters, etc. so that in the event of earthquake, they do not fall on the people.
5. Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings have fire fighting equipment in working order.

Measures to be taken in a house when earthquake occurs.

1. Take shelter under a table and stay there till shaking stops.
2. Stay away from tall and heavy objects that may fall on you.
3. If you are on bed, do not get up. Protect your head with a pillow.

Measures to be taken outdoors when earthquake occurs.

1. Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
2. If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop.

Activity – 6

Question 6.
Locating the tsunami affected areas in the map:
Take an outline map of the world. Locate the eastern coast and Andaman and Nicobar Islands in India. Mark other countries around the Indian Ocean which could have suffered damage.
Collect accounts of the devastation caused by the tsunami in India from your parents, or other elders in the family or in the neighbourhood.
Answer:

Devastation due to tsunami:

1. Loss of lives, families and friends.
2. Loss of properties.
3. Loss of jobs and living.
4. Emotional challenge.
5. Loss of livestock.
6. Dramatic or drastic changes to a whole community’s routine living.
7. Negative impact on the affected regions, economy.
8. Negative impact to the affected region’s tourism.

To the environment:

1. Alternation to seaside terrain.
2. Minor deforestation in the area effected by the tsunami.
3. Wild life casualities.
4. The sea will be temporarily littered with debris after the tsunami.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 5 Metals and Non-Metals

AP State Syllabus 8th Class Physical Science Important Questions 5th Lesson Metals and Non-Metals

8th Class Physical Science 5th Lesson Metals and Non-Metals 1 Mark Important Questions and Answers

Question 1.
What is meant by lustrous material?
Answer:
The material which show brightness on surface and reflect the light are called lustrous material.

Question 2.
What is malleability? Which materials have malleability?
Answer:
The property of material by which they can beaten into thin sheets is called malleability. Generally metals exhibit malleability property, e.g.: Iron, copper, etc.

Question 3.
What is ductility? Which materials show ductility?
Answer:
The property of drawing materials to make fine wires is called ductility. Generally metals show ductility, e.g.: Gold, copper, etc.

Question 4.
Have you observed materials used to make school bell or bells in temple ?
Answer:
Generally they are made up of metals.

Question 5.
Why do wooden bells not used in temple?
Answer:
Wood does not give a ringing sound when it is hit with a hammer. That means it does not show sonorous property. So wooden bells are not used in temple.

Question 6.
What is meant by sonorous?
Answer:
The ability to material to produce a particular sound when it is dropped on the hard surface is called sonorous.

Question 7.
Is ductility is the only property to use them as connecting wires in electric circuits?
Answer:
No, it is one of the cause. The other thing is metals are very good conductors of electricity. So they easily allows the passage of current. So they are used as connecting wires.

Question 8.
What does cooking appliances conduct?
Answer:
Cooking appliances conduct heat from heating device like gas stove or electric stove.

Question 9.
What is the nature of metallic and non-metallic oxides?
Answer:
Generally metallic oxides are basic in nature and non-metallic oxides are acidic in nature.

Question 10.
What happen when keep an iron rod in open place for one or two days?
Answer:
Rusting takes place on iron. The reason is iron react with air that contains oxygen and moisture forms a reddish brown coating (rust) due to formation of iron oxide.

Question 11.
Why do some metals do not get rust?
Answer:
Metal with very low reactivity do not react with air. So they do not get rust. They also called as noble metals, e.g.: Gold, platinum.

Question 12.
What happens when magnesium ribbon is exposed to air?
Answer:
It becomes dull when it is exposed to air due to formation of magnesium carbonate. That’s why magnesium ribbon should be cleaned with sand paper before any chemical reaction.

Question 13.
Why does silver objects and jewellery become black after sometime?
Answer:
Silver articles are black after sometime because they react with oxygen in air and form silver oxide.

Question 14.
Why statues and vessels made up of copper become dull green after certain time?
Answer:
The statues and vessels made up of copper became dull because they react with air and form copper hydroxide and copper carbonate which appears as dull green coating.

Question 15.
What happens when non-metals are added to water?
Answer:
They do not react with water.

Question 16.
How do you test hydrogen gas?
Answer:
If we place a burning match stick near a test tube containing hydrogen gas it puts out the match stick with pop sound and the gas burns with blue flame.

Question 17.
What happens when acids are added to non-metals?
Answer:
Non-metals do not react with acids.

Question 18.
What is a displacement reaction?
Answer: A more reactive metal displace a less reactive metal from its compound in aqueous solution is called displacement reaction.

Question 19.
Which metal has highest ductility?
Answer:
Gold. One gram of gold can be drawn into a wire of length one kilometre.

Question 20.
Why sodium and potassium are stored in kerosene?
Answer:
Sodium and potassium are highly reactive. They react vigorously with oxygen and water. A lot of heat is generated in the reaction. Therefore these metals are stored in kerosene.

Question 21.
Is all metals are hard?
Answer:
No. Sodium and potassium are soft. So they can be cut with a knife.

Question 22.
Which non-metal has lustrous surface?
Answer:
Iodine has lustrous surface.

Question 23.
Which non-metal is extremely hard?
Answer:
Diamond (allotrope of carbon) is extremely hard.

Question 24.
Why immersion rods for heating liquids are made up of metallic substances?
Answer:
Metals are good conductors of heat. So immersion rods for heating liquids are made
up of metals.

Question 25.
Why does copper cannot displace zinc from its salt solution?
Answer:
Copper is less reactive than zinc. So it cannot displace zinc from its salt solution.

Question 26.
Why does aluminium foils are used to wrap food items?
Answer:
It does not readily react with food items. So aluminium foils are used for wraping food items.

Question 27.
The doctor reported iron deficiency in my body. Where is iron in my body?
Answer:
Iron is present in haemoglobin. Which gives red colour to blood.

Question 28.
I heard that magnesium is found in plants. In what form is it found in them?
Answer:
Magnesium is present in chlorophill. It is in Mg(II) state.

Question 29.
Gold jewellery does not become dull. Why?
Answer:
Gold and platinum does not react with components of air. So, gold and platinum does not rust. So gold jewellery does not become dull.

8th Class Physical Science 5th Lesson Metals and Non-Metals 2 Marks Important Questions and Answers

Question 1.
What are physical properties of non-metals?
Answer:
Physical properties of non-metals:

1. They are non lustrous.
2. They are non sonorous.
3. They are soft.
4. They does not show malleability and ductility.
5. They are bad conductors of heat and electricity.

Question 2.
Is our body is a metal or a non-metal?
Answer:
Most of the human body is made of water (H₂O). It is not surprising that majority of a human body’s mass is oxygen. Carbon, the basic unit of organic molecules is the second. 99% of human body is made up of just six elements. Oxygen (65%), carbon (18%), hydrogen (10%), nitrogen (3%), calcium (1.5%), phosphorous (1%). Which shows our body has almost 97% of non-metals. So we may consider our body as non-metal.

Question 3.
Draw a diagram which shows metals are good conductors of electricity.
Answer:

Question 4.
Draw a diagram which show metals are good conductors of heat.
Answer:

Question 5.
Explain about ductility.
Answer:

1. Some materials cannot be drawn into wires.
2. Property of drawing a material to make fine wires is called ductility.
3. Most metals are ductile.

Question 6.
How do you appreciate the efforts of man to use the Metals in making tools?
Answer:

1. Early human beings made their tools from stone and wood.
2. Later they used the bones of animals.
3. Then they discovered metals like copper and iron.
4. Tools made of copper and iron are much stronger than tools made of stone and wood.
5. Metals had the advantage of not just being harder but they can be heated in a fire and moulder or cast into different shapes. So it became possible to make a wider range of tools with such metals.
6. Hence the efforts of man to use the metals in making tools appreciated.

Question 7.
You came to know that the Diamond is a hardest material and it is a non-metal and similarly Mercury is a soft material and it is a metal.Write down the questions raised in your mind.
Answer:

1. Are all metals hard?
2. Are there any non-metals hard like diamond?
3. Are there any metals soft like mercury?
4. What makes mercury so soft and diamond so hard?
5. Can we distinguish those metals and non-metals depending on their opposite properties like these examples?

Question 8.
Taking the example of magnesium and sulphur explain how metals and non-metals produce with different characteristics.
Answer:

1. Magnesium in the presence of oxygen burns to produce basic magnesium oxide. When it its added to water, it produces magnesium hydroxide, which turns the red litmus solution into blue.
2. Sulphur combines with oxygen, it forms acidic oxide. It get changed into sulphurous acid when react with water. This turns the blue litmus solutions into red.

Question 9.
What happens when
a) Dilute sulphuric acid is poured on a copper plate?
b) Iron nails are placed in copper sulphate solution?
Answer:
a) Copper sulphate is formed and hydrogen gas is released.
copper + dilute sulphuric acid → copper sulphate + hydrogen gas
b) Brown coating is deposited on the Iron nails. This is because of displacement of copper from copper sulphate solution by Iron.
Iron + Copper sulphate_(solution) → Iron sulphate_(solution) + Copper

8th Class Physical Science 5th Lesson Metals and Non-Metals 4 Marks Important Questions and Answers

Question 1.
What happens when magnesium, sulphur burnt in the presence of oxygen ? Write the word equation.
Answer:
When magnesium is burnt in the presence of oxygen it burns brilliantly and forms white ashes of magnesium oxide.

When sulphur is burnt in the presence of oxygen, it forms a yellowish gas called sulphur dioxide.

Question 2.
What are uses of various non-metals?
Answer:
Uses of non-metals:

1. Oxygen is essential for all living beings.
2. Nitrogen as fertilizer enhance the growth of plants.
3. Chlorine is used to purify the water.
4. Sulphur is used in making fire works, crackers, gun powder, match sticks and anticeptic ointments.
5. Activated carbon is used as decolourising agent and also in water purification systems.
6. Tincture iodine is used in medical purpose.

Question 3.
What are the uses of metals?
Answer:
Uses of metals:

1. Gold, silver, copper are used in making jewellery.
2. Silver foil is used in decoration of sweets.
3. Aluminium foil is used in inner packing of food materials and toffees.
4. Aluminium and copper mixture is used in currency coins, medals and statues.
5. Zinc and iron mixture is used in making of iron sheet.
6. Most of agricultural instruments are made by iron.
7. Electrical appliances, automobiles, satellites, aeroplanes, cooking utensils, machinery decorative materials are made by metals.

Question 4.
Prepare a table of various metals and non-metals used in our daily life and their usage.
Answer:

Metals/non-metals	Their usage
1) Gold	Jewellery
2) Silver	Jewellery
3) Copper	Jewellery, utensils, electrical appliances
4) Aluminium	Utensils, packing of food, aeroplanes, satellites
5) Iron	Utensils, electric appliances, agricultural tools
6) Iodine	Medical purpose
7) Chlorine	Purification of water
8) Nitrogen	Fertilizers
9) Sulphur	Gun powder, matchsticks, fire works, crackers, antiseptic ointments
10) Oxygen	Essential for all living things to live

Question 5.
The nature of oxides helps to identify the metals and non-metals conduct an experi-ment to prove this and record the observations.
Answer:
I) Aim: The nature of oxides helps to identify the metals.
Material required : Magnesium sample, spirit lamp, red litmus paper.
Procedure:

1. Take a small strip of magnesium and burn it and note the appearance after the reaction.
   Reaction: When we burn the sample of magnesium, it reacts with oxygen in air and form magnesium oxide.
   
2. Take magnesium oxide solution and place red litmus in it. Red litmus turns to blue indicates the solution is basic in nature.

Result: Metallic oxides solutions are basic in nature. So if the oxide solution is basic then the oxide is formed by a metal.

II) Aim: The nature of oxides help to identify the non-metals.
Material required: Sulphur sample, spirit lamp, blue litmus paper, deflagrating spoon. Procedure:

1. Take a small amount of sulphur powder in a deflagrating spoon and heat it.
2. As soon as sulphur starts burning, introduce the spoon into glass jar or tumbler.
3. Add small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well.
   Reaction: Sulphur burns and reacts with oxygen in air to give sulphur dioxide.
   
4. Place blue litmus paper in the prepared solution it turns to red indicates the solution is acidic nature.

Result: Non-metallic oxides solution are acidic in nature. So if oxide solution turns blue litmus into red then the oxide is formed by a non-metal.

Question 6.
Collect the information about metals which we Use in our daily life, and their uses. Write a report on it.
Answer:

1. The special properties of metals help us in many ways.
2. Metals are lustrous (shining). So, we make ornaments of gold and silver.
3. Metals are sonorous. So, we make school bells, temple bells, gongs, etc.
4. The malleability of metals help us to make sheets of iron, etc.
5. Ductility is the special character of metals which help us in making wires.
6. Metals conduct heat and electricity. Hence we make utensils for cooking and electrical wires etc.
7. Metals react with oxygen and produce oxides of basic nature.
8. Metals react with acids (dilute) and liberate hydrogen gas. So, in the preparation of hydrogen gas, metals come in use.
9. Non-metal like sulphur is used in making fire works, crackers, gun powder, matchsticks and antiseptic ointments.

Question 7.
Give reasons for the following.
a) Aluminium foils are used to wrap food items.
b) Immersion rods for heating liquids are made up of metallic substances.
c) Copper cannot displace Iron from its salt solution.
d) Sodium and potassium are stored in Kerosene.
Answer:
a) Aluminium has high malleability. So it is very easy to make aluminium foil compared other metals.
b) Because metals are good conductors of electricity.
c) Iron has more reactivity than copper. So copper cannot displace Iron from its salt solution.
d) Sodium and potassium have high reactivity with water and an even they burn in the presence of air and water. So these metals are stored in Kerosene.

Question 8.
Give reasons for the following.
i) Silver is used in making mirrors.
ii) Aluminium is used to make electrical wires.
iii) Sour food substances should not be stored in aluminium utensils.
iv) Iron is used in constructing bridges and houses.
Answer:
i) Silver has high reflecting power.
ii) Aluminimum is good conductor of electricity.
iii) Sour substances contain acids which react with aluminimum utensils to form toxic substances.
iv) Iron is hard, strong and rigid material.

Question 9.
Give some differences with examples between metals and non-metals with reference to their properties. Give one exception in each case.
Answer:
a) Lustrous: Metals have shining surfaces. So they are called Lustrous. Whereas non-metals have dull surface so they are non Lustrous.
One of the form of carbon is diamond has most shining look.
Iodine a non-metal also has lustrous surface.
b) Malleability: Metals can be beaten into sheets and non-metals cannot be beaten into sheets. But mercury is a metal which breaks into pieces when hammered.
c) Ductility: Metals are drawn into wires. Non-metals cannot be drawn into wires. Mercury does not show ductility.
d) Conductivity: Metals are good conductors of heat and electricity and non-metals are bad conductors of electricity and heat. Graphite is a non-metal which is good conductor of heat and electricity.
e) Hardness: Metals are usually hard and non-metals are soft. But sodium and potassium are quite soft, they can be cut by using a knife. Diamond is a non-metal which is the hardest substance.

8th Class Physical Science 5th Lesson Metals and Non-Metals Important Questions and Answers

Question 1.
Predict the reason behind gold and platinum jewellery does not become dull.
Answer:
Gold and platinum does not react with components of air. So, gold and platinum does not rust. So gold jewellery does not become dull.

Question 2.
Write any two differences between electric conductors and insulators.
Answer:

Electric conductors	Electric insulators
1) Those substances through which electricity can flow are called conductors.	1) Those substances through which electricity cannot flow are called insulators.
2) Generally metals are conductors. Eg: Silver, copper	2) Generally non-metals are insulators. Eg: Rubber, plastic, glass

Question 3.
Write any four uses of metals in different situations.
Answer:
Uses of metals:

1. Gold, silver, copper are used in making jewellery.
2. Silver foil is used in decoration of sweets.
3. Aluminium foil is used in inner packing of food materials and toffees.
4. Aluminium and copper mixture is used in currency coins, medals and statues.
5. Zinc and iron mixture is used in making of iron sheet.
6. Most of agricultural instruments are made by iron.
7. Electrical appliances, automobiles, satellites, aeroplanes, cooking utensils, machinery decorative materials are made by metals.

Question 4.
Explain the reaction of metals with acids.
Answer:
Aim: To find the reactivity of metals with acids.
Apparatus: Test tube, dilute hydrochloric acid, magnesium ribbon, spirit lamp. Procedure:

1. Take a magnesium ribbon and rub with a sand paper.
2. Put this ribbon into a test tube containing dilute hydrochloric acid.
3. A gas is evolved from the test tube.
4. Now bring a burning match stick near the mouth of the test tube.
5. The gas puts off the match stick and produces a pop sound and gas burns with blue flame.
6. Which indicates hydrogen gas is released.
7. We will get same results with zinc, iron, copper also.
8. Conclusion: Metal reacts with acid and produce hydrogen gas.

Question 5.
Explain a procedure to do the experiment that magnesium ribbon allows the flow of current.
Answer:
Procedure:

1. Arrange ah electric circuit with a battery and bulb.
2. Close the circuit using a magnesium ribbon.
3. Observe whether the bulb is glow or not.

Observation: Bulb glows.
Conclusion: Magnesium ribbon allows the flow of current.

Question 6.
Suggest an activity to show that the magnesium ribbon reacts with Oxygen to form Magnesium Oxide, which is basic in nature.
Answer:
Aim: To know reaction of oxygen with metals.
Material required: Magnesium strip, spirit lamp or Bunsen burner and litmus papers, distilled water.
Procedure:

1. Take a small strip of magnesium.
2. Burn it with spirit lamp.
3. It burns brilliantly and produce white ashes of magnesium oxide due to reaction between magnesium and oxygen.
4. Collect the ash of magnesium in a watch glass and add some distilled water.
5. Test the solution with red litmus paper and blue litmus paper.

Observation: Red litmus paper turns into blue in colour.
Conclusion: Metallic oxide solutions are basic in nature.

Question 7.
Zinc, Copper, Sulphur, Carbon, Categories into these into metals and non-metals and write their uses.

S.No.	Name	Metal/Non-metal	Use
1. 2. 3. 4.

Answer:

S.No.	Name	Metal/Non-metal	Use
1.	Zinc	metal	sheets, batteries
2.	Copper	metal	electrical wires, jewellary, Utensils
3.	Sulphur	non-metal	Gun powder, fireworks, ointments
4.	Carbon	non-metal	Water purifiers, fuel

Question 8.
You are given copper sulphate, Iron sulphate, an iron nail and copper wire. How do you test the reactivity of metals iron and copper Explain through an activity.
Answer:
Activity:

1. Take two beakers ‘a’ and ‘b’.
2. Take 50 ml of water in each.
   
3. Dissolve some amount of copper sulphate in beaker ‘a’ and iron sulphate in beaker ‘b’.
4. Drop iron nails in beaker ‘a’ and copper wire in beaker ‘b’.
5. Leave the beakers for some hours.

Observations:
i) In beaker ‘a’ copper layer forms on the iron nails and blue colour of copper sulphate turns pale blue or white.
ii) No change in beaker ‘b’.
Conclusion:
i) Copper is displaced by iron in beaker ‘a’.
Copper Sulphate + Iron → Iron sulphate + Copper
ii) Iron is not displaced by copper in beaker ‘b’.
Hence iron reactivity is more than copper.

Question 9.
Draw a diagram of an activity of heat conduction by metals. Why iron, copper and aluminium are used to prepare in the manufacturing of cooking vessels?
Answer:

Iron, Copper and aluminium cooking vessels are preferred due to their high heat conductivity.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 12 Stars and the Solar System Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 12th Lesson Stars and the Solar System

8th Class Physical Science 12th Lesson Stars and the Solar System Textbook Questions and Answers

Improve Your Learning

Question 1.
What is your local noon time?
Answer:
The time when the shortest shadow of a vertical object occurs in a particular place is called local noon time at that place.

Question 2.
Where do you find moon at night?
a) 2 days before Poumami
b) 2 days after Amavasya
Answer:
a) Couple of days (2 days) before full moon day (Pournami), a crescent is seen in the west just after sunset.
b) Couple of days (2 days) after the new moon day (Amavasya), a crescent is seen in the west just after sunset.

Question 3.
Why doesn’t eclipse occur on every full moon day or on every new moon day?
Answer:
Lunar eclipse can happen during a full moon and only when the moon and earth and sun are directly in line and the moon passes through the earth shadow. Most of the time the moon is slightly out of line and that is why we don’t have a Lunar eclipse every full moon.

Question 4.
Where do you find the pole star?
Answer:
The pole star lies on the line joining the two outer stars of the constellation great bear. Pole star directly above the north pole of earth.

Question 5.
What Is the difference that you find between pole star and other stars?
Answer:
If we observe the position of various stars constantly. We will notice that they are not in a fixed position because as the earth rotates about a fixed axis, the position of stars with respect to earth changes. But the position of pole star does not change with respect to earth.

Question 6.
Why does polestar seem to be stationary?
Answer:
The polestar is situated in the direction of the earth’s axis and that is why it does not appear to move even though all stars appear that they are moving because of ie rotation of earth. So pole star seems to be stationary.

Question 7.
Name some constellations.
Answer:
Names of some constellations:

1. Great bear (Saptarishi)
2. Cassiopeia (Sharmistha)
3. Orion
4. Leo (Simha)
5. Corona
6. Borealis

Question 8.
How many planets are there in our solar system? What are they?
Answer:
There are 8 planets in our solar system. They are:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus and
8. Neptune.

Question 9.
Look at the below table and name the smallest and the biggest planets in our solar system.

Answer:
From the table the biggest planet is Jupiter and the smallest planet is Mercury.

Question 10.
Among all 8 planets what is the special thing about earth?
Answer:
The special thing about earth is it is the only planet in the solar system on which life is exist.

Question 11.
How do day and night occur?
Answer:
The day and night occur due to rotatory motion of earth.

Question 12.
Do the stars appear moving? How can you say?
Answer:
Yes, stars are appear moving. Our galaxy like all other spiral galaxies is rotating. The stars move on orbits around the centre of the galaxy. It was the motions of stars in external galaxies that lead to the idea of dark matter in the universe. Stars also have some random motions. They do not orbit galaxy in exact circles. As observers we see this motion of the stars as what is called proper motion, the projection of their velocity on to the plane of the sky is radial motion.
Normal Answer : Alternate answer is No. All the stars appears that they are moving because of rotation of earth.

Question 13.
Is it possible to see the polestar for the people who live in the southern hemisphere of the earth? Why?
Answer:
A pole star is a visible, preferably a prominent one, that is approximately aligned with the earth’s axis of rotation. The term polestar refers to polaris which is the current northern pole star also known as the north star. So the people in southern hemisphere unable to see this pole star.

Question 14.
What is the use of artificial satellites in our daily life?
Answer:
Artificial satellites have many uses in daily life.

1. They are used for forecasting weather.
2. They are used for transmitting television and. radio signals.
3. They are also used for telecommunication.
4. They are used in aviation and military (these satellites are called remote sensing which will collect information from a distance).

Question 15.
Why is Venus the brightest planet?
Answer:
Venus is very bright that’s partly because sunlight easily reflected by acidic clouds that blanket the planet atmosphere and also it is closest planet to earth.

Question 16.
Are you curious about going to the moon? Why?
Answer:
Yes, I am curious about going to moon. Because I want to find answers raised in my mind.

1. Is it true there is no life on moon?
2. If it does not have atmosphere, how it look like?
3. How earth look like from moon?
4. Whether there are any mountains on moon or not?
5. There may be any creators on moon or not?
6. Whether there is any form of water exists on moon?
7. Whether we able to walk on moon as freely as on earth surface?

Question 17.
While observing the shadow of a stick from morning to evening, some questions arose in Ramya’s mind. What may be those questions?
Answer:

1. Why sun is changing its position from morning to evening?
2. How does the length of the shadow change with time?
3. Why we are getting longest shadows in the morning and evening?
4. Why the shadow in the noon is shortest?
5. Do all the days at noon have same size of shadow?

Question 18.
What are the questions that engage your mind when you look at night sky?
Answer:

1. Is stars collide with each other?
2. Where does the stars go in the morning?
3. Whether stars daily travel in the same path?
4. Why night sky is black and early morning sky is blue?
5. Whether we can count stars in the sky?
6. Why stars grouped to form constellations?

Question 19.
Even though we do not have clock, we can know the time by observing some shadows in daytime. Think and discuss with your friends how we can know the time at night?
Answer:
We can know the time by position of moon and stars or with reference to pole star. Estimation of time by using position of moon:

1. If the moon is full do the experiment stop if it is new moon.
2. Imagine the moon is divided into 12 vertical strips. First hour at right edge and last hour at left edge. It can vary by season or location.
3. Read the moon from left to right following an imaginary horizontal half line.
   Look for where the line intersects the boarder between light and dark. Make a note of which strip that intersection is in.

For example:
The instruction is at 8 pm and transition from right to left is from light to dark. This tells us the moon will set in the west at 8 pm.
This moon will set at about 7-8 hours after sunset. If sunset is at 8 pm. You can expect moon time is at 3-4 am.

Question 20.
How can you find north – south direction at your place?
Answer:
This experiment should be performed on a day when the sky is clear, preferably between nine in the morning and four in the evening.

Pick a spot in open ground away from buildings and trees. The spot should be as flat as possible.
Take a stick which is a little over a meter long and fix it vertically in the ground. Ensure that exactly one meter of stick remains above the surface of ground. Build a fence around your stick as shown in figure.
Make your first observation at nine in the morning, Make a mark with a nail or peg at the point where the tip of the shadow falls on ground. Measure the length of the shadow.
Then, make similar observations for every half an hour throughout the day till four in the evening.
Find the direction of shortest shadow cast by vertical object on the ground. That gives the north-south direction.

Question 21.
In which direction (towards north or south) is the sun moving day by day when you read this lesson?
Answer:
From December 21 to till June 21 the sun appears to shift northward. From June 21 to December 21 the sun appears to shift southward.
(Basing on this information we have to give the answer suppose you have read the lesson in the month of February the sun is moving towards north direction).

Question 22.
What are the planets you have seen in the sky? When do you observe those planets?
Answer:
The two planets observe in the sky are

1. Venus: Sometimes Venus appears in the eastern sky before sunrise. Sometimes it appears in the western sky just after sunset. Therefore it is often called a morning or an evening star.
2. Mars: It appears slightly reddish and therefore, it is also called red planet. It appears in the east.

Question 23.
What is the duration of a day and night today? Collect the information about duration of day and night for the past 7 days from the newspapers, analyze it and say whether summer or winter is going to come.
Answer:
Students have to collect the information from newspaper and other resources.
(Hint: If sun is shifting towards south the upcoming season is winter if it is shifting towards north the upcoming season is summer).

Question 24.
What are the other districts on the same latitude as your district ?
Answer:
I am residing at Krishna district. The latitudes of Krishna district are 16. The other districts which have same latitude are West Godavari, Mahaboobnagar.
(You should write the latitude of your district and you have to find out the districts which lie in that latitude from table -1 on page 163 of textbook.)

Question 25.
Collect the information about cosmic dust (wastage) from newspapers, internet and make a poster on your school panel board about the consequences of cosmic dust.
Answer:
Cosmic dust: Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 mm in size.
Consequence of cosmic dust:
The orbit of space junk could deteriate resulting in the junk falling to earth. If it survives and reaches the earth’s surface it would cause the same damage as equally sized meteorite, including damaging or destroying structures in the area killing people, etc.
The earth receives hundreds of tonnes of space dust, rocks, etc every week. If you were to get whole load of it in one place and try and breathe it in it probably would be harmful. However natural concentrations are so low that it possess no risk.

Question 26.
Make a sundial. Explain how you made it.
Answer:
Making of sundial:
Cut a right angled triangle ABC from a sheet of cardboard. Angle C of the triangle should equal to the latitude of your city or town and angle A should be 90° as shown in figure.

Fix cardboard triangle vertically in the middle of a rectangular wooden board. Glue strips of paper along both edges of BC and the wooden board to make the triangle stand erect.
Place your board with the triangle on level ground in an open space which gets sunlight throughout the day. Base BC of the triangle should be placed in the north- south direction, with B pointing to the north.
At nine in the morning, draw a line along the shadow of side AC on the wooden board. Write the time along side of the line. Draw lines of the shadow of side AC at one hour intervals through the day till sunset and mark the time for each line. The sundial is now ready.

Question 27.
Draw the different phases of moon. Arrange them in an order from poumami to amavasya.
Answer:

Question 28.
Draw the location of polestar showing the direction from Great Bear.
Answer:

Question 29.
Draw the diagram of the solar system.
Answer:

Question 30.
How do you appreciate the construction of knowledge about the universe by our ancestors?
Answer:
They study of our universe changed from time to time from earth is flat to higgs bosan particles. All these secrets about our universe are revealed due to constant afforts of our ancestors. That is due to construction of knowledge about the universe by our ancestors. So the afforts of our ancestors should be thoroughly appreciated.

Question 31.
We launched so many artificial satellites around our earth for different purposes. What do you think about the impact of artificial satellites and their radiation on bio-diversity?
Answer:
Effect of radiation released from artificial satellites on biodiversity:
I. Animals and humans:

1. Killing certain enzymes in the body can simply make sick.
2. If radiation damages DNA, the body may not repair it. It increases the chances of both animals and humans developing cancer.

II. Marine animals: High level of radiation cause a reduction and reproduction capabilities of marine animals.
III. Plants: Weaking of seeds and frequent mutations. Excess of radiation killing plants.

Question 32.
Among eight planets of our solar system, earth is the only planet supporting life. Explain how we should protect our earth and its environment.
Answer:
Steps to be taken to protect earth and environment:

1. Reduce pollution by reducing air, water and land pollution.
2. Recycle resources by sending the degradable like paper and non degradable like plastic and glass objects to recycling factory.
3. Save resources by using them carefully. E.g.: Water, trees, wood, paper.
4. Stop burning fossil fuels (Coal, oil and natural gas) for that do not waste electricity.
5. Plant lot of trees.

8th Class Physical Science 12th Lesson Stars and the Solar System InText Questions and Answers

8th Class Physical Science Textbook Page No. 160

Question 1.
What are the celestial objects that we can see in the sky?
Answer:
Stars, Planets, Moon (Satellite), Comets, Meteors and Meteorites are the celestial objects that we can see in the sky.

Question 2.
Are the stars moving?
Answer:
Yes, the stars are moving.

Question 3.
Do you see the same stars at night and early in the morning?
Answer:
No, we do not see the same stars at night and early in the morning.

Question 4.
Do you see the same stars during summer and winter nights?
Answer:
Yes, it is due to the change of axis of rotation of the earth.

Question 5.
What is the shape of the moon? Why does it change? Why doesn’t the sun change its shape daily like the moon?
Answer:
The actual shape of the moon is approximately spherical.
But it changes everyday.
The sun does not change its shape like the moon due to its size and the distance it is away from the earth. Moreover the shadow of the earth falls on one side of the moon partially or fully. This makes the changes in its shape. Also the moon does not have its own light to make the shadow of the earth to fall on the huge sun.

Question 6.
Where exactly is the sun situated in the sky at noon?
Answer:
Above our head (vertically above) (Really the sun does not revolve around the earth but due to the rotation and revolution of the earth we feel / imagine that the sun moves around the earth.)

Question 7.
Why does the shadow of a tree change from morning to evening?
Answer:
Due to the rotation of the earth we find the sun at different positions in the sky which brings the tree the different shadows from morning to evening.

8th Class Physical Science Textbook Page No. 168

Question 8.
Will we be able to hear any sound if we were on the moon? Why?
Answer:
Sound required a medium for its propagation. There is no atmosphere (medium) on moon. We know sound cannot travel in vacuum. So we unable to hear any sound if we were on the moon.

Question 9.
Can any life exists on the moon? Why?
Answer:
Moon does not have air (oxygen) and water which are essential for existence of life. So there is no life exists on moon.

8th Class Physical Science Textbook Page No. 169

Question 10.
Why does lunar eclipse occur only on a full moon day?
Answer:
Lunar eclipse occur only on a full moon day because lunar eclipse happen when the earth’s shadow falls on the moon, hiding it from the sun’s light. For this to happen, the moon must be on the opposite side of the earth from the sun. So the full half of the moon that is lit by the sun is visible from earth that is full moon day.

Think and Discuss

8th Class Physical Science Textbook Page No. 161

Question 1.
Look at the nails or pegs you have fixed on the ground to keep track of the shadow of the stick throughout the day. From their positions, can you tell how the position of the sun changes in the sky from sunrise to sunset?
Answer:
The position of sun changes from slanting to vertical and then vertical to slanting.

8th Class Physical Science Textbook Page No. 163

Question 2.
Why does the sun appears to travel towards north or south? Try to find the answer by reading your social studies chapter “Earth movements anti seasons” along with this lesson.
Answer:
The earth’s tilt is constant 23.5 degree perpendicular. The earth position relative to sun changes, not the tilt itself during orbit. The sun is moving towards north throughout summer because the north pole is tilted 23.5 degree towards sun and we are in northern hemisphere. During the winter the south pole is tilted 23.5 degree so the sun appear to travel towards south.

8th Class Physical Science Textbook Page No. 168

Question 3.
Scientists are planning to build settlements on moon and are trying to make arrangements to live there. You know that there is no air on moon. How will it be possible to live on the moon then?
Answer:
Oxygen is essential for humans. Unless we built special structures and buildings on the moon and put oxygen into them, we would not able to live on the moon without wearing oxygen tanks all the time.

8th Class Physical Science Textbook Page No. 178

Question 4.
The diameter of the sun is 13,92,000 Km. The diameter of the earth is 12,756 Km. The diameter of the moon is 3,474 Km. The distance from the sun to earth is 15,00,00,000 Km. The distance from the earth to moon is 3,84,399 Km.
Take the scale as 1 lakh km = 1 cm, and imagine how the arrangement of sun, earth and moon is in our universe. Can you make this arrangement on your school ground?
Answer:
Yes, we can do it in our play ground. Placing sun at the middle. Rotating earth around sun and rotating moon around earth by measuring diameters in cm.

8th Class Physical Science 12th Lesson Stars and the Solar System Activities

Activity – 1

Question 1.
Observing the changes in the length of shadow.
This experiment should be performed on a day when the sky is clear, preferably between nine in the morning and four in the evening.

Pick a spot in the open ground away from trees and buildings.
The spot should be as flat as possible. Take a stick which is a little over a meter long and fix it vertically in the ground. Ensure that exactly one meter of stick remains above the surface of ground.
Make your first observation at nine in the morning. Make a mark with a nail or peg at the point where the tip of the shadow falls on ground. Measure the length of the shadow.
Then, make similar observations for every half an hour throughout the day till four in the evening.
Use a clock to fix the time for making your observations. Enter the measurements of the length of the shadow and the time of measurement in a table making two columns, one for time and another for length of shadow.

Time	Length of the shadow
9.00 am	1.75 m
9.30 am	1.7 m
10.00 am	1.6 m
10.30 am	1.5 m
11.00 am	1.1 m
11.30 am	0.8 m
12.00 noon	0.7 m
12.30 pm	0.81 m
1 pm	1.12 m
1.30 pm	1.3 m
2.00 pm	1.5 m
2.30 pm	1.75 m
3.00 pm	1.84 m
3.30 pm	2.2 m
4.00 pm	2.5 m

(These values are changes from place to place and with seasons)
a) Look at your table and figure out the time of the day of shortest shadow.
Answer:
I observed at 12 noon.

b) When did you observe the longest shadow in your activity?
Answer:
At 4 pm.

c) How does the length of the shadow change with time? Illustrate your answer with the help of some diagrams. Draw the diagrams of the stick and its shadow for 5 different times, that is, at 9am, 1 lam, 12noon, 2pm and 4pm.
Answer:
The size of the shadow decreases and reach a minimum and then increases (It has minimum value at 12 noon)
(Students have to draw the diagrams of the stick and its shadow at 9 am, 11 am, 12 noon, 2 pm and 4 pm by doing this activity)

d) If you continue your activity from sunrise to sunset, at what times do you think the shadow would be the longest?
Answer:
At sunrise and at sunset.

e) Where is the sun situated in the sky at noon? Where does the shadow of stick is fall at that time? Think about how your own shadow will be at that time.
Answer:
Almost in line with the stick. It will falls in north-south direction. My own shadow is also in north-south direction.

f) Do you think that your shadow length will be the same on all the days at noon?
Answer:
Yes, the shadow will be same on all the days (with in two weeks).

g) In which direction does the shortest shadow of the stick fall in your activity?
Answer:
The shortest shadow falls in the north-south direction.
Continue your observations.

h) Observe on the next day whether the shadow of the stick falls at the same spots at the same times throughout the day.
Answer:
Yes, it falls on the same spot.

i) Can you use your stick as a clock (sundial) to tell the time? If your answer is ‘yes’, explain how this is possible.
Answer:
Yes, due to movement of sun from east to west.

j) Two weeks later, once again check to see whether the stick’s shadow falls at the same spots at the same times during the day.
Answer:
It fall on the same spot. But length of shadow change.

k) If the shadow does not fall on the same spot, what could be the possible reason?
Answer:
The position of the sun in the sky changes during the day.

l) If you continue the experiment the position of shadow changes or not ?
Answer:
No, it does not change. The position of sun changes from day to day as well.
That is, the position of the sun at 10.00 am today will be different from its position two weeks later at the same time. If you choose a particular time every week and mark the position of the sun with a peg at that time, you can build a calendar for the full year.

m) During a period of two weeks you had made an observation that the length of the shadow at a particular time is changing day by day. Did it become longer or shorter?
Answer:
Yes, it is changing day by day. During summer it is shorter day by day and during winter it is larger day by day.

n) By observing the direction of shadows, can you guess the arrival of summer or winter?
Answer:
Yes.

Activity – 2

Question 2.
Understanding the north-south movement of the sun.
Fix a spot near your home from where you can observe the sunrise. You may have to go to the terrace of a RCC building or go to an open field for the purpose. Choose a tree or an electric pole or some other stationary object as a reference point.

Over the next 10 to 15 days, note the spot at which the sun rises daily, keeping in mind your reference point. Make a daily sketch of the rising sun as well as your reference point in your notebook during this period.
a) Does the spot of sunrise change? If it does, in which direction does it seem to move?
Answer:
It may moves towards south of the sky if it is Dakshinayanam or it may moves towards north of the sky if it is Uttarayanam.
(So answer based upon Uttarayanam or Dakshinayanam)

b) Was the sun appear travelling towards south or north during the time you made your observations?
Answer:
It is travelling towards north.

c) Do you think that is the reason for the change in the length of the shadow of the stick day by day in activity 1 ?
Answer:
Yes, that is the reason.

d) Assuming that you did not have any calendar and knowledge of months and seasons, can you use movement of the sun to predict the arrival of winter or summer?
Answer:
Yes, if it is moving towards north, the coming season is summer (in the above case it is summer) and if it is moving towards south, the coming season is winter.

Activity – 3

Question 3.
Make your own sundial.
Answer:
First of all, you will need to cut a right angled triangle ABC from a sheet of cardboard. Angle C of the triangle should equal to the latitude of your city or town and angle A should be 90° as shown in figure.

A list of latitudes of districts of Andhra Pradesh is given below in table.

Fix your cardboard triangle vertically in the middle of a rectangular wooden board. Glue strips of paper along both edges of BC and the wooden board to make the triangle stand erect.
Place your board with the triangle on level ground in an open space which gets sunlight throughout the day. Base BC of the triangle should be placed in the north- south direction, with B pointing to the north.
At nine in the morning, draw a line along the shadow of side AC on the wooden board. Write the time along side the line. Draw lines of the shadow of side AC at one hour intervals (use a clock to check the time) through the day till sunset and mark the time for each line. Your sun-dial is ready.

Activity – 4

Question 4.
Observing phases of the moon.
a) Have you ever observed the movement of moon in the sky?
Answer:
Yes.

b) Does the moon appear at same point at a particular time everyday?
Answer:
Yes.

c) s the shape of the moon same on everyday?
Answer:
No, it changes.

Now note the date of the day after new moon day (amavasya), when the moon first appears in the sky.
Also note the time at night when the moon sets (goes down in the western sky). In the same way everyday locate the moon in the sky at the time of sunset or immediately after sunset.
Record the date and time of the moon set and draw a picture of the moon as you see it on that day in your notebook as shown in figure.
Continue making observations for as many nights as possible.
Observe the moon a few days before full moon day (Pournami) to a few days after it. Locate the position of moon in the sky at the time of sunset before Pournami and note the time and position of moon in the sky at that time.
After Pournami, note the time at which the moon rises (comes in the eastern sky) and also note the date. Draw pictures of the shape of the moon each of these days.

d) Can you calculate the number of hours between one moon rise and the next moon rise or the number of hours between one moon setting and the next moon setting, with help of these observations?
Answer:
It is about 24 hours and 50 minutes.

e) How many hours lapse between one sunrise to the next, or one sunset to the next?
Answer:
It is about 24 hours.

f) Is the time period same for sun and moon to appear at selected position after completing a cycle in the sky every day?
Answer:
No, they are different.

g) Does the moon appear at the same point every day during the time of the sunset?
Answer:
No.

h) What is the shape of the moon? Is it same every day?
Answer:
It is changing day by day.

i) You might have observed that the shape of the moon changes night after night. What is the name given to these changes in appearance ?
Answer:
These changes in its appearance are called the phases of the moon.

j) Can you guess why the shape of the moon changes?
Answer:
The time period taken by sun to complete a cycle in the sky and come to the selected position is almost same everyday and it is about 24 hours i.e., 1 day. Whereas moon takes about 50 minutes more than a day to complete the cycle and which results in the phases of moon.

Activity – 5

Question 5.
A Moon-shaped lemon.
Answer:
Choose a day one week after the new moon day when the moon is visible in the sky during the day time.
Take a yellow lemon or a whitewashed clay ball and pivot it on a long needle or on a spoke of bicycle. Hold it up towards the moon as shown in figure.

Ensure that you are standing in the sun¬shine when you do this activity.
Observe the shape formed by the sunlight on the surface of the lemon. Is there some similarity between the shape formed and the shape of the moon?
It forms one of the phase of moon.

Activity – 6

Question 6.
Why does the shape of the moon change ?
(Do this activity around 4p.m.)
Wrap a ball tightly with a white hand-kerchief or with a piece of white cloth.
Assume this is the moon. Hold this ball in front of your eyes in bright sunshine as shown in figure and turn around yourself slowly. Observe how the shape of the illuminated part of the ball changes.

a) Does sunlight fall on half the ball at all times while you turn around?
Answer:
Yes.

b) Is the shape of the illuminated part on the ball viewed by you same in all positions during your rotation?
Answer:
No, they are different.

c) Why does this happen?
Answer:
To understand this look at figure.

c) Why does this happen?
Answer:
To understand this look at figure.

The large circle in the middle of figure is the earth and the smaller circles around it represent the moon in different positions. We can see the phases of the moon on different days in the figure. The sunrays falling on the moon illuminate half its surface in all the positions. However, we cannot see the entire illuminated surface in all the positions. In some cases we see the entire illuminated surface while in others we see only part of it. In one particular position, we cannot see the illuminated surface at all.
The shape of the moon we see is the shape of the illuminated portion visible to us.
In figure, the day of the new moon is called day 0 or day 28 (position 1). In this position, the illuminated surface is not visible from earth, so the moon cannot be seen from earth.
Four days later, when the moon is in position 2, a small part of its illuminated surface is not visible from earth. On day-7, the moon is in position 3, so more of its illuminated part is visible from earth.
After fourteen days (at position 5) the entire illuminated surface of the moon is visible from earth. This is the day of the full moon.
Subsequently, the moon appears smaller with each day as it passes through positions 6 (day-18), 7(day-21) and 8(day- 25). After 28 days, the moon is once again in position 1.
Try to duplicate position 1 with the ball. For this, you will have to hold the ball towards the sun (between your eyesight and the sun).

d) In this position, which half of the ball is illuminated?
Answer: Although half the surface of the moon is illuminated everyday, we cannot see the moon on new moon day since the illuminated surface is on the side opposite to the point of observation on the earth. On a full moon day, the situation is reversed. The illuminated half of the moon faces the point of observation, so we see a full moon.

e) Where is the position of sun and moon on new moon day and full moon day?
Answer:
The sun and moon must be on the same side of the earth on a new moon day and they are on opposite sides of the earth on a full moon day.

f) Can you now state as to in which direction the moon will rise on a full moon day?
Answer:
The moon will rise from west on full moon day.
While we observe moon in clear sky on a full moon day, we think about the spots those are visible on the moon. In olden days people are curious about the spots. This led to creation of a lot of stories.

e) Do you know any such story?
Answer:
One popular story to account for the dark spot on the moon is that Ganesha, once filled with food, fell from his mouse and broke his stomache. Chandra laughed at this, at which Ganesha injured him by breaking off and throughing one of his tusks and cursed him.

Activity – 7

Question 7.
Observing the movement of constellations (stars).
Take a 20cm x 20cm square sheet of paper and make a 1cm diameter hole in its center. Mark a cross ( X ) on one side of the sheet of paper as shown in figure.

Hold the sheet in front of your eyes with the ‘X’ mark at the bottom and look for the pole star through the hole. Once you have located the pole star, check in which direction the Great Bear and Cassiopeia lie.
Write ‘G’ for Great Bear and ‘C’ for Cassiopeia on the paper in the directions in which you see each of the constellations. Mark the timing at which you made your observation in both cases.
Choose a nearby tree or house as a reference point. Draw a picture of your reference point on the paper sheet taken, clearly indicating its location. Repeat your observations at one hour intervals. Ensure that you are standing on the same spot each time you look at the stars.
Write G, C in the direction of the position of the great bear and Cassiopeia during each observation and note the time of the observation next to the letters G and C.
Using the tree or house you have chosen as your reference point, check whether the position of the pole star has changed or not. If it has changed, note the changed position.
Repeat this activity as many times as possible, the minimum being four times. But ensure that the ‘X! mark on your sheet of paper remains at the bottom during all your observations.

a) Do the positions of the stars change with time?
Answer:
Yes, they will change.

b) Does the position of the pole star also change with time?
Answer:
No, it will not change with time.

c) Does the shape of the great bear and Cassiopeia change with time or does the position of the entire constellations in the sky change?
Answer:
The position of entire constellation changes.

d) What kind of path do these constellations trace in the sky?
Answer:
They traced in northern sky.

Activity – 8

Question 8.
Why does the pole star appears fixed at one point?
Take an umbrella and open it. Make about 10-15 stars out of white paper. Paste one star at the position of the central rod of the umbrella and others at different places on the cloth near the end of each spoke.

Now rotate the umbrella by holding its central rod in your hand. Observe the stars on the umbrella.
a) Is there any star which does not appear moving? Where is this star located? Is it located where the rod of the umbrella holds the cloth of the umbrella?
Answer:
Yes, it is located where the rod of the umbrella holds the cloth of the umbrella.

b) On similar lines, if there were a star located where the axis of rotation of the earth meets the sky, could this star is also be stationary?
Answer:
Yes, that is the reason pole star does not move even though all stars appear that they are moving because of rotation of earth.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 10 Reflection of Light at Plane Surfaces Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 10th Lesson Reflection of Light at Plane Surfaces

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces Textbook Questions and Answers

Improve Your Learning

Question 1.
State the laws of reflection of light (OR)
Name the laws of reflection of light
Answer:
Laws of reflection:

1. When light gets reflected from a surface, the angle of reflection is equal to the angle of incidence, i.e., ∠i = ∠r.
   
2. The incident ray, the normal at the point of incidence and the reflected ray lie in the same plane, i.e., AO, ON, OB are in same plane.

Question 2.
How do you verify the 1st law of reflection of light with an experiment?
(OR)
Raghu found that for a plane mirror angle of incidence is equal to the angle of reflection. Write the experiment to prove this fact. (OR)
Prove: ∠i = ∠r (LAB ACTIVITY – 1)
Answer:
Aim: Verification of first law of reflection.
Required materials: Mirror strip, drawing board, white paper, pins, clamps, scale and pencil.
Procedure:

1. Take a drawing board and fix a white paper on it with the help of clamps.
2. Draw a straight line AB at the centre of the paper and also a normal (ON) to AB at the point ‘O’.
3. Draw a straight line PQ making certain angle (angle i) with ON.
4. Fix two pins at P and Q on the paper vertically.
   
5. Observe the images of pins – P’ of the pin P and Q’ of the pin Q, in the mirror kept along the line segment AB.
6. Fix two more pins R and S such that they are in the same line as that of P’ and Q’.
7. Join R, S and 0 as shown in figure.
8. Measure the angle between RS and ON (angle of reflection).
9. We will find that ∠i = ∠r. (angle of incidence = angle of reflection)
10. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.
11. We can find angle of incidence = angle of reflection in all these cases.
    Thus first law of reflection is proved.

Question 3.
How do you verify the 2nd law of reflection of light with an experiment?
(OR)
John found that incident ray, reflected ray and normal drawn to surface lie on the
same plane. What are the apparatus required for this experiment? How are you able to prove this fact experimentally?
Answer:
2nd Law of reflection: The incident ray, the reflected ray and normal all lie in the same plane.

1. As shown in the figure, a light ray incident on a plane mirror and touches at a point ‘O’. Here AO is called incident ray.
2. When a ray of light falls on a mirror, the mirror sends it back in another direction OB. Here OB is called reflected ray.
3. Normal is a line which is perpendicular to the mirror at the point of incidence. So the line ON’ is the normal to the mirror surface at point ‘O’.
   
4. Here the incident ray (AO), the reflected ray (OB) and the normal (ON) all lie in the same plane of the paper.
   Hence 2nd law of reflection is proved.

Question 4.
Explain the image formation by pin hole camera with the help of the diagram.
(ACTIVITY – 1)
Answer:

1. Draw a ray diagram of the formation of an image in a pinhole camera.
2. Observe the flame of a candle with a pinhole camera making a big hole to it.
   
3. We can understand that the light rays coming from the top of the candle flame fall at different points on the screen.
4. Similarly, the rays coming from bottom of the candle points on the screen.
5. Thus, we get blurred image on the screen due to the big hole of the camera.

Question 5.
Find the plane of the reflection experimentally for the incident ray which passes through the heads of the pins pierced in front of the mirror.
(OR)
Sudheer wants to verify the laws of reflection. What apparatus he requires to prove them? State the laws of reflection and write the experimentation process he follows.
Answer:
Aim: Verification of laws of reflection.
Required material: Mirror strip, drawing board, white paper, pins, clamps, scale and pencil.
Procedure:

1. Take a drawing board and fix a white paper on it with the help of clamps.
2. Draw a straight line AB at the centre of the paper and also a normal (ON) to AB at the point ‘O’.
3. Draw a straight line PQ making certain angle (∠i) with ON.
4. Fix two pins at P and Q on the paper vertically.
   
5. Observe the image P’ of the pin P and Q’ of the pin Q, in the mirror kept along line segment AB.
6. Fix two more pins R and S such that they are in the same line as that of P’ and Q’.
7. Join R, S and O.
8. Measure the angle between RS and ON (∠r) .We will find ∠i = ∠r.
9. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.
10. We find that each case angle of incidence is equal to angle of reflection. That is first law.
11. We can find that the incident ray is the ray which is passing through points P and Q touching the paper.
12. The reflected ray is the ray which is passing through the points R and S touching the same paper and ON is the normal to the mirror at O. All lie in same plane. That is second law which states incident ray, reflected ray and normal drawn to plane lie in the same plane.

Question 6.
Have you ever observed the image of the sky in rain water pools on earth? Explain the reflection of light in this context.
Answer:
Surface of the rain water pool acts as a plane mirror, because of its smooth surface. The light rays from the sky and clouds incident at this surface and reflect. Hence, the images of the sky and clouds appear in the rain water pools.

Question 7.
Discuss the merits and demerits of using mirrors in building elevation.
(OR)
What are the advantages and disadvantages of using mirrors in building elevation?
Answer:
Merits:

1. The mirrors used in elevating building are tough, reinforced and laminated glasses so they provide safety to the building.
2. They make the building attractive.
3. They absorb heat energy, so they cool inside the building.
4. If we use plane mirrors in building elevation it is easy to wash with water and no need of regular painting.

Demerits:

1. Elevation of buildings with mirrors is not suggestable.
2. These mirrors reflect sun rays at day time and reflects lighting from near by electrical bulbs at night time, which causes confusion and disturbance for the vehicles and people who are running on the nearby roads lead to accidents.
3. Birds like sparrows, crows will get confusion while flying on roads.
4. They are also not safe enough to the buildings, which causes easy access to thieves.
5. This glass elevation is not environmental friendly, because natural air does not enter into the building.
6. They are easy to break and cause cuts and wounds.

Question 8.
If a ray incidence normally on a plane mirror, what will be the angle of reflection.
Answer:
If a ray incidence normally on a plane mirror, the angle of reflection will be zero.

Question 9.
Why does the image in plane mirror suffers lateral inversion?
Answer:
The light rays which come from our right side get reflected from the plane mirror reach our eye. Our brain feels that the rays is coming from the inside of the mirror. That is why our right side looks like left side in the image. This is called right-left inversion or lateral inversion.

Question 10.
Draw a ray diagram to understand the formation of image for a pointed object by a plane mirror explain it.
Answer:
Observe the figure. ‘O’ is a point object.

Some rays from ‘O’ reach the mirror and get reflected. When we look into the mirror, the reflected rays seem to be coming from the point T. So, point I is the image of point object ‘O’.

Question 11.
In the adjacent figure, AO and OB are incident and reflected rays respectively angle ∠AOB = 90°. Find the values of angle of incidence and angle of reflection.

Answer:
We know that angle of incidence is equal to angle of reflection.
i = r …….. (1)
From the figure, ∠AOB indicates i + r = 90°
From (1)
⇒ i + i = 90°
2i = 90°
⇒ i = 90/2 = 45°
⇒ i = r = 45°
Angle of incidence i = 45°; Angle of reflection r = 45°.

Question 12.
Hinduja stands in front of a plane mirror at a distance of 5 m. from the mirror and observes her image in the mirror. If she moves 2 m. towards the plane mirror, then what will be the distance between Hinduja and his image?
Answer:
The distance between plane mirror and Hinduja = 5 m
The distance between plane mirror and Hinduja after moving 2 m towards mirror
= 5 – 2 = 3 m …….. (1)
The distance between plane mirror and Hinduja’s image after moving = 3 m …….. (2)
The distance between Hinduja and her image after moving = (1) + (2) = 3m + 3m = 6m.

Question 13.
Explain diagramatically the Image of letter ‘B’ in a plane mirror.
Answer:

Question 14.
Why can’t we see our image in a white sheet of paper though it reflects light?
Answer:
By microscopic observation, we can find up and downs over surface of a paper. Hence paper is not a smooth fine surface. Even though sheet of white paper reflects the light rays, they do not form an image of an object.

Question 15.
Observe the below figure. AB and BC are two plane mirrors arranged at 120°. A ray incidents at and angle 55° on AB. Find the value of ‘x’

Answer:
Let us say, angles a, b, c, d as shown in the figure. From the figure, a = 55° [∵ i = r]
a + b = 90° [. Normal to the plane]
55° + b = 90°
⇒ b = 90° – 55° = 35°
120° + b + c = 180° [∵ Total of angles in a triangle]
120° + 35° + c = 180°

⇒ c = 180° – 155° = 25° c + d = 90° [∵ Normal to the plane]
25° + d = 90°
⇒ d = 90° – 25° = 65°
d = x [∵ i = r]
∴ x = 65°

Question 16.
The size of the image in the mirror seem to be decreased when you move the object towards your eye from the mirror. Draw the diagram showing angles depicting the situation.
Answer:

Question 17.
Collect the information about “Situations using the plane mirrors and prepare the report.
Answer:
Plane mirrors have many uses.

1. Periscopes: They are used in periscopes to see bends and corners. It is used for observing enemy movements from trenches without any danger of being seen. Sailors on submarines use periscopes to see things above the water level.
2. Kaleidoscopes: Kaleidoscope is a toy that uses light and mirrors to reflect objects and create beautiful, fascinating repeating patterns.
3. Security: Mirrors are used while looking for explosives underneath a vehicle. Even these mirrors are used in shops to keep an eye on the customers. Mirrors are also used in blind turns of busy roads to see the vehicles coming from the other side.
4. Telescopes and Microscopes: Plane mirrors are used in many scientific applications like telescopes and microscopes.
5. Dressing mirrors: Plane mirrors are used in dressing tables to see ourselves, while dressing, shaving, etc.
6. Ophthalmic doctors: They use plane mirrors to increase the distance of the eye test chart while examine the eye of a patient.
7. Docorating mirrors: Plane mirrors are used to decorate the building for elivations. Some shops also used plane mirrors to get multiple images of the items in their shops.

MULTIPLE CHOICE QUESTIONS
1. Angle of incidence = Angle of reflection. This rule is explained by …………… principle        ( )
A) Fermat
B) Newton
C) Archemedes
D) Pascal
Answer: A

2. Which of the following letters doesn’t suffer lateral inversion?         ( )
A) C
B) O
C) B
D) N
Answer: B

3. A ray of light incidents on a plane mirror at an angle of 90° to its surface. What will be the angle of relfection?   ( )
A) 0°
B) 90°
C) 450°
D) 180°
Answer: A

4. If we move an object away from the plane mirror the size of images seems to be     ( )
A) increases
B) decreases
C) of the same size
D) image can’t be seen
Answer: B

5. Which of the following is incorrect with respect to the image in a plane mirror?     ( )
A) Image is erect
B) size of the image is same as the size of object
C) laterally inverted
D) image is real.
Answer: D

6. An object is placed 7cm distance from the plane mirror then distance of image is      ( )
A) 3.5 cm
B) 14 cm
C) 7 cm
D) 21 cm
Answer: C

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces InText Questions and Answers

8th Class Physical Science Textbook Page No. 134

Question 1.
How can we get the image of a big building in a small mirror?
Answer:
Light rays travel in all directions from one object. Light rays coming from a building incident on the small area of a plane mirror and reflect. These reflected rays reach our eye. We see the image of the building in the mirror.

Question 2.
Can we get the image formed by a plane mirror on a screen?
Answer:
Cannot.

Question 3.
Why is there lateral inversion, when we look into a mirror?
Answer:
Our brain feels that the rays is coming from the inside of the mirror.

Question 4.
Why is the angle of reflection equal to the angle of incidence when a light ray gets reflected from a surface?
Answer:
Light always choose the path of least time to travel.

8th Class Physical Science Textbook Page No. 138

Question 5.
Is the angle of reflection equal to the angle of incidence in all cases?
Answer:
Yes.

Question 6.
Do the two rays and the normal lie in the same plane? If yes, which is that plane?
Answer:
Yes, plane of paper.

Question 7.
In which plane will the incident ray, reflected ray and the normal lie?
Answer:
Plane touching the heads of pins and parallel to the plane of paper.

Question 8.
How will the incident ray be?
Answer:
Incident ray touching heads of the pins (P and Q) and make some angle with plane of the paper.

Question 9.
How will the reflected ray be?
Answer:
Reflected ray will make some angle with plane of the paper.

Question 10.
How will the normal be?
Answer:
The normal will also make same angle as incident and reflected rays.

Question 11.
How will the plane of reflection be?
Answer:
Plane of reflection make some angle (which is equal to plane of the paper and incident ray) with plane of the paper.

Question 12.
How does a mirror form the image of a pin or any object? Let us discuss.
Answer:
The rays coming from the pin get reflected from the mirror and seem to be coming from the image in the mirror.

8th Class Physical Science Textbook Page No. 139

Question 13.
What is the size of the image compared to the size of the object?
Answer:
Size of the image is equal to size of the object.

Question 14.
What do you say about the size of the image compared to the size of the object? Move the object towards your eye. What do you observe?
Answer:
Size of the image is same as size of the object. If we move the object towards our eye, size of the image of the object seems to be decreased.

Question 15.
Is the size of the image decreasing or increasing?
Answer:
Decreasing.

8th Class Physical Science Textbook Page No. 140

Question 16.
Why does an image suffer lateral (right-left) inversion? See the figure.

Answer:
Our brain feels that the rays are coming from the inside of the mirror and image is opposite to us. In this way image suffer lateral inversion.

Question 17.
What do you understand from the figure?
Answer:
The light rays which come from our right ear get reflected from the plane mirror and reach our eye. Our brain feels that the ray is coming from the inside of the mirror. That is why our right ear looks like left ear in the image.

Think, Discuss and Write

8th Class Physical Science Textbook Page No. 135

Question 1.
Does the explanation on pinhole match with your observation?
Answer:
Yes, it matches with my observation.

Question 2.
What happens if the hole Is much bigger, i.e., equal to the size of the flame?
Answer:
The image is extremely blurred.

Question 3.
If so, can we get the image of flame on the screen of pinhole camera? Why?
Answer:
No. Because the light rays coming from the top of the flame and bottom of the flame fall at different points on the screen. So it is blurred and is not formed on screen.

Question 4.
What happens if we observe the same flame with the same pinhole camera from a long distance?
Answer:
We may observe not only the flame, but the blurred image of entire candle.

Question 5.
What happens if we made two holes to pin hole camera?
Answer:
Two images will be formed.

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces Activities

Activity – 2

Question 1.
Which grain on the ground that a smart crow on tree A pick to reach B in short time (Shortest path)? Explain. (OR)
How do you support your answer to “When light gets reflected from a surface, it selects the path that takes the least time”? (OR)
Explain Fermat’s principle by using an activity.
Answer:

1. The crow can pick the grain from any point on the ground, but the condition is selecting the shortest path.
2. Let the speed of the crow is constants –
3. Observe some of the paths in figure.
4. To compare the lengths of these paths ACB, ADB, AEB and AFB, make the duplicates of them at point G as shown in figure.
5. In the figure CB = CG,
   ∴ The length of path ACB = AC + CB = AC + CG = ACG
6. Similarly length of the path ADB = length of the path ADG Similarlylength of the path AEB = length of the path AEG Similarly length of the path AFB = length of the path AFG
7. By observing the above paths, we will notice that AEG is the shortest path among all the paths, because it is the straight line distance between points A and G.
8. So the smart crow will pick the grain from point E.

Activity – 3

Question 2.
Look at the following figure.
Suppose if you have been given a plane mirror strip, what will you do to obtain figures as shown below figure (b) using mirror strip and the above figure (a)?

Answer:
The place of mirror that should be place on the figure vertically has been shown here under by a line.

In the above diagrams, line indicates the position of mirror to be kept to get the required shapes.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 9 Electrical Conductivity of Liquids Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 9th Lesson Electrical Conductivity of Liquids

8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids Textbook Questions and Answers

Improve Your Learning

Question 1.
Give examples for good solid conductors and liquid conductors.
Answer:
Examples for good conductors in solids:
Silver, copper, iron, graphite, etc.
Examples for good conductors in liquids:
Mercury, acid solutions (HCl, H₂SO₄), base solutions (NaOH, KOH), salt solutions (NaCl, KCl), etc.

Question 2.
Give examples for bad solid conductors and liquid conductors.
Answer:
Examples for poor conductors in solids:
Gold, platinum, etc.
Examples for bad conductors in liquids:
Distilled water, coconut oil, petrol, vegetable oil, kerosene, alcohol, etc.

Question 3.
What do you add to distilled water for making it to conduct electricity?
Answer:
Distilled water is poor conductor of electricity. In order to increase conductivity we should have to add either acid, base or salt. That will increase the conductivity of distilled water due to decomposition of these substances into constitute ions.

Question 4.
What is an electrolyte ?
Answer:
Electrolyte is a solution of substance through which current can pass.

Question 5.
Which energy is cause for glowing of bulb in electrolytic cell?
Answer:
Electrolytic cell is a device which converts chemical energy into electrical energy. So chemical energy stored in the cell is cause for glowing of bulb.

Question 6.
Write the uses of electroplating.
Answer:
Uses of electroplating:

1. Metals like iron are coated with deposits of nickel or chromium to prevent rusting.
2. Machinery parts are often chromium plated to protect them from corrosion and at the same time to give them good polish.
3. Electroplating is also used in repairing worn out parts of machinery.
4. Electroplating is also done for ornamentation and decoration purposes.
5. Processed food items are preserved in tin coated iron cans by electroplating method.
6. Zinc coated iron by electroplating method is used for bridges and in automobiles.

Question 7.
In case of a fire, before the fire men use the water, they shut off the main electrical supply for the area. Explain why they do this.
Answer:
Fire men use water to put out fire. Water containing dissolved salts is a good conductor of electricity. If fire men pour water on fire the electrical appliances near the fire may be wet if anybody touches those appliances they may have electric shock. In order to avoid people to get electric shock due to wet electrical appliances the fire men shut off electrical supply before they use water.

Question 8.
We get some items made from iron wire in which iron wire is coated with plastic. Is plastic coated by the process of electroplating? Why plastic cannot be coated on a metal by the process of electroplating?
Answer:
No. Plastic cannot be coated on a metal by using electroplating. The reason is plastic being a carbon polymer does not dissociate into ions. So it does not allow passage of current. So it does not act as an electrolyte. So electrolysis process is not possible with plastic which is main criteria for electroplating. So plastic cannot be coated on a metal by the process of electroplating.

Question 9.
Kavya observed that a discharged dry cell which kept in sunlight by her father for few hours got ability to glow LED. She got many doubts and questions to raise. Can you guess those questions or doubts? (OR)
Rohan observed that a discharged dry cell which kept in sunlight by his brother for few hours got ability to glow LED. He got many doubts and questions to raise. Guess the doubts or questions.
Answer:

1. Why does the bulb glow?
2. How does the dry cell charged?
3. Which energy is useful in charging the discharged dry cell?
4. Shall we use that energy to get rid from electrical power cut?

Question 10.
Explain the process of coating copper on iron key. Draw the circuit diagram.
(OR)
Conduct an experiment for coating on iron key with copper by electroplating method and prepare a note.
Lab Activity
Answer:
Aim: Coating an iron key with copper by electroplating method.
Required material: Copper plate of size 2 cm x 5 cm, crystals of copper sulphate, a key made by iron, glass beaker, water, sulphuric acid, battery cell and some connecting copper wires.
Procedure: Dissolve crystals of copper sulphate in pure water to prepare concentrated solution. Pour the solution in a beaker and add a few drops of dilute sulphuric acid to it.

Tie one end of connecting copper wire to iron object to be coated with copper. Connect other end to the negative terminal of battery. Suspend the tied iron object into the copper sulphate solution. Suspend the copper plate into copper sulphate from positive end of the battery through a switch as shown in the above figure. Key and plate are a little away from each other. Put the switch on for about 10 minutes. Switch the circuit off and take the iron key out.
We can observe a red coating on iron key. The reason is when electric current is pass through copper solution, in which copper sulphate is present in the form of copper and sulphate ions. The copper ion gets drawn to the electrode connected to the negative terminal of the battery and deposited on it.

Question 11.
How do you appreciate the efforts of Luigi Galvani and Alessandro Volta in discovering a cell and making a stored electric energy available to human beings?
Answer:
We should have to thoroughly appreciate the efforts of Luigi Galvani and Alessandro for their discoveries for the development of mankind. Galvani and Volta completely change the life of human beings. Before that people generated electricity in different ways and conduct various experiments. However they faced one major problem which prevented them from understanding electricity in depth. They did not have a stable and permanent source of electricity. Galvani experimental conclusion was a revolution in science saying that all living beings contained electricity and it was the main source of life.
Volta proved it is possible to generate electricity if two different metals are placed in some liquids. Volta made first cell using zinc and copper dipped in sulphuric acid. This cell called Volta cell. Later dry cell was prepared. Now various appliances works with dry cells. So the efforts of Galvani and Volta should be appreciated by every generation for their contribution to electricity.

Question 12.
Collect the information and make a list of good conductors and bad conductors. Mow do you use this information in your daily life works?
Answer:

Good conductors	Bad conductors
1) Metals	1) Wood
2) Acid solutions	2) Plastic
3) Base solutions	3) Diamond
4) Salt solutions	4) Distilled Water

Applications in daily life: This information is very useful to us. Generally metal or good conductors of electricity are used in electrical appliances, electrical wires, fuse wires, etc. Whereas plastic is a bad conductor is used for electric insulators like gloves, handles of electrical appliances etc. to avoid electric shocks.

Question 13.
Make a battery from four lemons and test it with a LED in the circuit.
(OR)
Write how do you make a battery from four lemons and test it with a LED in the circuit in your laboratory.
Answer:
Take four lemons cut them into two pieces. Take one piece from each lemon and insert two copper wires and connect them in series and connect a LED and complete the circuit. The circuit is shown below.

The bulb glows due to presence of current in the circuit. Here lemon juice acts as electrolyte and copper wires acts as electrolyte. So each lemon piece dipped with a copper wire acts as cell. These cells connected in series forms a battery.

Question 14.
Refer to the activity 3 in this chapter. Start with distilled water. The LED would not glow. Add two drops of some acid to distilled water and check the glow of LED. Add two more drops and check the intensity of the glow. Repeat the activity 5 to 6 times by adding 2 drops of the same acid each time. Do you see any difference in the intensity of glow with increasing acid content of water? What can be inferred from the above observations? Repeat the entire activity by taking a solution of baking soda and adding drops of it to distilled water instead of acid. Write differences and similarities.
Answer:
When we add two drops of acid (namely hydrochloric acid) to distilled water the LED will glow. If we further add the acid another two drops the intensity of glow increases. By repeating same activity 5 or 6 times we observe every time the glow of LED increases. The reason is acid dissociate into ions in aqueous solution. Which allows the passage of current. As the quantity of acid increases there will be more ions available for passage of electricity. So the intensity of glow increases.
We will observe the same result by adding baking soda but the intensity of glow is some what less when compared with addition of acid. The reason is baking soda is a weak base. So the dissociation is less when compared with acid. So less ions are available for passage of electricity. So the intensity of glow of LED is less when compared with acid.

Question 15.
In many of the activities in this chapter, we have used a tester made up of LED. Can we avoid LED and use something else as a tester Magnetic compass needle could be an alternative tester. We know that when we take a current carrying wire near magnetic compass needle, it shows deflection. Use this property to make a tester of magnetic compass needle. You may refer to the following figure.
Answer:
A magnetic compass wound with a copper wire is connected to one end of dry cell. The other end is connected to one of the two metal pins separated by a small gap in a rubber cap. The second pen is connected to the other end of dry cell to completed the circuit.

The magnetic needle deflects because whenever current pass through a wire it acts as a magnet is called magnetic effect of current.

8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids InText Questions and Answers

Think and Discuss

8th Class Physical Science Textbook Page No. 123

Question 1.
Why some material allows electric current to pass through them and why some do not?
Answer:
Flow of charged particles constitutes current. So for the passage of current the material should have charged particles. All the materials do not have charged particles, e.g. Plastic, wood, diamond, etc. So only those material which have charged particles allow passage of current.

8th Class Physical Science Textbook Page No. 127

Question 2.
If a battery is packed in a box and if only two wires from two terminals are given out, how can we decide the positive and negative terminal of the battery?
Answer:
Insert the wires into a potato. A greenish spot is seen on potato at one of the wires. That wire behave like positive terminal and the other is negative terminal.

8th Class Physical Science Textbook Page No. 129

Question 3.
What is electrolysis?
Answer:
The dissociation of a solution of compound into constitute ions or elements by passing current is called electrolysis.
e.g. Electrolysis of water, which produce oxygen and hydrogen gases.

8th Class Physical Science 9th Lesson Electrical Conductivity of Liquids Activities

Activity – 1

Question 1.
Testing the material to know which allows electric current to pass through it.
Answer:
Take a torch bulb or LED (Light Emitting Diode), a dry cell, wooden sheet, two drawing pins, a key (safety pin) and pieces of connecting wires. Set up the electric circuit as shown in the figure.

Place the key on drawing pin. The bulb begins to glow as soon as the key touches the drawing pin. Now replace the key by a nail.
Does the bulb glow ?
Yes, the bulb glows.
Repeat the activity using different types of materials instead of the nail, say a strip of paper, a piece of chalk, a drinking straw, a piece of plastic, a paper clip, a rubber eraser, etc.
Note in each case whether the bulb glows or not and enter your observations in table.

Object	Material	Bulb glows Yes/No	Good conductor/ bad or poor conductor
Nail	Iron	Yes	Good conductor
Eraser	Rubber	No	Bad or poor conductor
Paper	Cellulose	No	Bad or poor conductor
Chalk	Calcium carbonate	No	Bad or poor conductor
Straw	Plastic	No	Bad or poor conductor
Plastic	Plastic	No	Bad or poor conductor
Matchstick	Wood	No	Bad or poor conductor

From the above activity, we conclude that some material allow electric current to pass through them. What we call them?
They are called good conductors of electricity.
The material that do not allow current to pass through them, what is the name given to those material?
They are named as bad or poor conductors of electricity.

Activity – 2

Question 2.
Testing the electric conductivity of liquids.
(OR)
Conduct an experiment for testing the electric conductivity of liquids.
Answer:
Take a LED, dry cell, metal pins, rubber cap of injection bottle and wires for making connections. Set up an electric
circuit shown in the figure.

See that the two metal pins, pass through the cap and should have a very small gap (around 2 mm) between them so that the pins are fairly closer but not touching each other. The LED should not glow when pins are separated by small distance.
Now, join the free ends of pins together by pressing them for a moment and make sure that the LED glows. Release the pins they get separated and LED should not glow. This acts as a tester.
Fill the rubber cap with different liquids like distilled water that we drink, coconut oil, kerosene, lime juice, mustard oil, sugar solution, etc one after another and in each case check whether the LED glows or not. Note down your observations in table.

Liquid	LED glows	Good conductor/ poor or bad conductor
Distilled water	No	Bad conductor
Drinking water	Yes	Good conductor
Coconut oil	No	Bad conductor
Lemon juice	Yes	Good conductor
Vinegar	Yes	Good conductor
Kerosene	No	Bad conductor
Vegetable oil	No	Bad conductor
Sugar solution	No	Bad conductor
Common salt solution	Yes	Good conductor
Milk	No	Bad conductor

a) Why doesn’t the LED glow in all the cases? Or why doesn’t the LED remain off in all the cases?
Answer:
The LED doesn’t glow all the cases because when the liquid the two pins of tester allows electric current to pass through, the circuit is completed (closed) and the LED glows. On the other hand when the liquid does not allow the current to pass through, the circuit is incomplete (open) and the LED does not glow.

b) In the above activity, you may have observed that in all those cases where the LED glows, its brightness (intensity) is not the same. Sometimes it may be brighter and sometimes it may be relatively dimmer. Why is that so?
Answer:
The intensity of the glow of the LED depends on the flow of electric current through the circuit. Although a liquid may be a conductor, it may not allow current through it as easily as a metal does.
As a result although the circuit is completed and the LED glows, due to weak current in case of some of the liquids, the intensity of glow would be lower compared to other liquids.

Activity – 3

Question 3.
Transforming a poor electric conductor into a good conductor.
(OR)
Conduct an experiment for testing the electric conductivity of electrolyte.
Answer:
Take some amount of distilled water in three different containers. Dissolve small quantity of common salt in the water of first container. Dissolve the copper sulphate, lemon juice in second and third container respectively.
Use the tester that we used in activity 2, and repeat the activity 2. Note the observations in table.

Material ‘	Does the LED glow? Yes/No	Good conductor/bad conductor
Distilled water	No	Bad conductor
Distilled water + salt	Yes	Good conductor
Distilled water + CuSO4	Yes	Good conductor
Distilled water + lemon juice	Yes	Good conductor

a) From table what can we infer?
Answer:
Distilled water does not allow the electric current to pass. Water in its pure form is a bad conductor of electricity. But when water contains salts or acids, it allows a passage of electric current and turns into a good conductor of electricity.

b) Do you understand why you are advised not to touch electric appliances with wet hands?
Answer:
Water with salts is a good conductor of electricity and the current flowing through househt d electric appliances is very high. Therefore we should never touch the electrical appliances with wet hands.

Activity – 4

Question 4.
Testing the effect of electric current on potato.
Take a potato. Cut into two halves and take one half of it. Construct tester with LED bulb. Insert two copper wires of the tester into the potato. Leaving some distance (around 1 cm) between them.

a) Dose the LED glow?
Answer:
Yes, the LED glows.
Leave the inserted wires for 20-30 minutes.

b) What do you observe the surface of the potato?
Answer:
A greenish blue spot is seen on the potato around the wire connected to the positive terminal of the battery.
But no such spot is seen around the other wire connected to the negative terminal. This greenish spot is due to chemical change in the potato.

c) What could be the cause behind this change?
Answer:
There is chemical change occurred in the potato.

d) Will other vegetables also show such an effect?
Answer:
Vegetable like carrot, beetroot, cucumber, radish, sweet potato show the chemical change there by the LED glows.

Activity – 5

Question 5.
Make your own cell.
(OR)
Draw the diagram of electrolytic cell and explain.
Collect two injection bottles. Cut two 5 cm long bits of thick copper wire. Use sandpaper to scrap about 1 cm of the coating off both ends of the wires.
Break open a exhausted dry cell and remove its outer metal covering (made of zinc). Cut two 2 mm wide and 5 cm long strips from this zinc plate. Insert the copper wires and zinc strips into the rubber caps of the injection bottles as shown in figure. Ensure that the copper wire and zinc strips do not touch each other.

Now take a wire and connect the copper wire of one bottle with the zinc plate of the other bottle. Fill both bottles with dilute sulphuric acid. Carefully close the bottles with the caps in which copper wires and zinc strips are inserted. Your cell is ready.
How will you test it?
Take an LED. Attach two wires to its two terminals. Touch the wire from one terminal to the zinc plate and the wire from other terminal to the copper wire. Did the LED light up ? If not, change the connections vice-versa. Did the LED glow ?
Repeat the above activity using lemon juice, tamarind juice and tomato juice one by one instead of sulphuric acid to make cells.

a) What other liquids can be used to make the cell?
Answer:
Acid solutions.

b) Will detergent solution be useful?
Answer:
Yes, it is useful.

c) How does above cell function?
Answer:
After a few seconds of immersion of zinc and copper into dilute sulphuric acid, zinc slowly begins to dissolve in the sulphuric acid. We can see bubbles getting formed on the copper rod.
The current is passed from copper rod to zinc rod. Here chemical energy is converted into electric energy by electrolysis method.

d) Can you compare this cell with dry cell?
Answer:
In the above cell electrolyte is dilute sulphuric acid whereas in dry cell ammonium chloride paste is electrolyte. The electrodes in above cell is copper and zinc, whereas in dry cell it is graphite (carbon) and zinc.

e) Which is good one? Why?
Answer:
Dry cell is better than ordinary Volta cell. The reason dry cell does not have any fluids. So it is easy to carry dry cell compared with volta cell. So dry cell is better than volta cell.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 4 Synthetic Fibres and Plastics

AP State Syllabus 8th Class Physical Science Important Questions 4th Lesson Synthetic Fibres and Plastics

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics 1 Mark Important Questions and Answers

Question 1.
What is polymer?
Answer:
Many small identical units combine to form a large unit is called polymer. The small units are called monomers.

Question 2.
What are synthetic fibres?
Answer:
The fibres obtained from petrochemicals when they are subjected to chemical processes are called synthetic fibres.
Have you ever heard a cracking sound when you take off certain type of clothes? or did you see sparks in them when it is dark?

Question 3.
What is the reason?
Answer:
This is static electricity developed by artificial fibres due to friction.

Question 4.
Why does wearing nylon clothes are not preferable while cooking or working near a fire?
Answer:
Nylon fibre easily catches fire. So it is not preferable to wear it while cooking, welding, working near a fire.

Question 5.
What is blending and what is the advantage of blending?
Answer:
Any synthetic fibre can be combined with two or more other fibres is called blending.
When two fibres are blended the resultant blended fibre possess the best qualities of both.

Question 6.
What are the uses of plastics?
Answer:
Plastics are used in milk and oil pouches, containers to store pickles and rice, buckets to store water, chairs, water pipes, electrical appliances, television, radio and comput¬ers and mobile phones.

Question 7.
What material is used to make handles of utensils?
Answer:
Bakelite is used for making handles of various utensils due to its poor conductivity of heat and electricity.

Question 8.
How do you appreciate 4R principle?
Answer:
4R principle is useful in developing ecofriendly environment and bright future for next generation of people.

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics 2 Marks Important Questions and Answers

Question 1.
How is nylon made? What are the advantages of nylon as fibre?
Answer:
Nylon is a polymer made of chemical units called polyamides.
Advantages of nylon as fibre:

1. Nylon fibre is strong, elastic and light weight.
2. Cloth made of nylon are lustrous and easy to wash.
3. Nylon does not absorb water.

Question 2.
Where does we use nylon?
Answer:
Nylon can be used in tooth brush bristles, ropes, fishing nets, tents, sarees, stockings and socks, car seat belts, sleeping bags, curtains, carpets and also used in making parachutes.
Rock climbers use nylon ropes to climb mountains. It is also used in making of swim suits, sheer hosiery, sails, umbrella cloth, dress materials, car tyres, etc.

Question 3.
How would you prepare rayon?
Answer:
The cellulose that was collected from wood or bamboo pulp is treated with sodium hydroxide and then carbon disulphide. It forms a syrup called viscose. Viscose is forced through a spinneret into a solution of dilute sulphuric acid. This gives us silk like threads. This new fibre is called rayon which is an artificial silk.

Question 4.
What are the uses of rayon?
Answer:

1. Rayon is cheaper than silk and can be woven like silk fibre.
2. Rayon is mixed with cotton to make bed sheets.
3. Rayon is mixed with wool in making of carpets.
4. Rayon is often used in fashion and home furnishings.
5. Rayon is also found in sanitary products, diapers and bandages and lints for dressing wounds.

Question 5.
What is acrylic ? Where do we use acrylic?
Answer:
Acrylic is a synthetic fibre made from the combination of coal, air, water and lime¬stone. It looks like natural wool. If can be considered as artificial wool.
It is used in knitted apparels such as fleece, socks, sportswear and sweaters. It is also used in craft yarns, upholstery fabric, carpets, luggage yawning and vehicle covers.

Question 6.
What are the advantages of natural fibre over artificial fibres?
Answer:
When natural fibres, contribute to a fabric it allows the skin to breathe easily. Also natural fibres are generally free from irritating chemicals. Whenever fire accidents takes place they does not stick to the body.

Question 7.
How do you prepare polyester? What are the advantages of polyester as fabric?
Answer: Polyester is made by reacting dicarboxylic acid with dihydric alcohol.
Advantages :

1. Polyester can be melted and spun. This property allows the fibre to convert into different sizes and shapes.
2. They are altra thin, microfiber which gives them a smoothen and soft feel.
3. They does not get wrinkled easily.
4. It remains crisp and easily washable.

Question 8.
Give example for popular polyester and what are its advantages?
Answer:
The popular polyester is terylene.

1. It can be drawn into very fire fabric fibres.
2. Terylene is after mixed with cotton to form terricot with wool to give terriwool. Which has best qualities of both blunded fibres.

Question 9.
What are plastics? How many types of plastics are there? Explain them with examples.
Answer:
Organic polymers are called plastics. Plastics are two types :

1. Thermoplastics: The plastics which get deformed easily on heating and can be bent are called thermoplastics, e.g.: Polyethene, PVC.
2. Thermosetting plastics: The plastics which molded once cannot be softened on heating are called thermosetting plastics, e.g.: Bakelite, melamine.

Question 10.
Where do we use bakelite?
Answer:

1. Bakelite is used for making handles of various utensils.
2. It is used for making electrical appliances including switch boards.
3. It is an alternative for pearl and jade.
4. In manufacture of telephone.

Question 11.
Where do we use melamine?
Answer:

1. Melamine is used in making of utensils and other grocery of kitchen.
2. It is used for making of floor and dress material (firemen dress) for their nature of fire resistance.
3. Computer and T.V. cabinets are made by melamine.

Question 12.
Ramu observing his grandmother keeping pickles in plastic bottles. What are the questions raised in his mind by seeing this?
Answer:
The questions raised in Ramu’s mind

1. Whether plastic is cheap when compare with metal?
2. Why does she not put the pickles in metal containers?
3. Whether metal containers react with pickles? If so they form harmful substances?

Question 13.
What do you know about creator of first man made plastic? How he prepare the plastic?
Answer:
The creator of first man made plastic is Alexander Parkes the name of the plastic is parkesine.
To prepare this material Parkes heated nitrated cotton which previously soaked in sulphuric acid and made fabric soft and elastic with oil and camphor. The end product was an ivory – coloured material that became distorted when subjected to heat. This is named as Parkesine.

Question 14.
What do you know about father of plastic industry? What are his major inventions and discoveries?
Answer:
Dr. Baekeland is considered as the father of present plastic industry. He was respon¬sible for the invention of bakelite. He accidently discovered the compound of carbolic acid and formaldehyde. When he tried to reheat the solidified compound he discovered it would not melt, no matter how high the temperature would be.

Question 15.
List out the objects made up of Acrylic.
Answer:

1. It is used in knitted apparels such as fleece, socks, sports wear and sweaters.
2. It is also used in craft yarns, upholstery fabric, carpets, lugguage awnings and vehicle covers.

Question 16.
Draw and explain the diagram of Universal recycling symbol.
Answer:
When the number is omitted from recycling icon then it is known as Universal recycling symbol.

Question 17.
What are thermosetting plastics? Give two examples.
Answer:
Thermosetting plastics are synthetic materials which gain strength during moulding by heating, but cannot be remoulded or reheated after their initial heat, moulding.
Ex : Bakelite and melamine.

Question 18.
What made the human beings to search for the alternative for natural fibres?
Answer:
Human being is always going in search of new things which can make his life more comfortable and durable. As the natural fibres are not durable, elastic or light weight or lustrous or easy to wash, he needed an alternative to fulfill his expectations. The solution to his expectations is synthetic fibre.

Question 19.
Imagine what would happen if we do not discover plastics.
Answer:
Nowadays every object used in our day to day life is made of plastic. For example milk and oil pouches, containers to store pickles and rice, buckets to store water, chains, water pipes, electrical appliances, television, radio and computers, mobile phones.
So plastics has taken over the place occupied by metal wood and glass items due to its special properties. So we cannot imagine our life without plastics because it is part of each and every aspect of life.

Question 20.
What is the most common material used in making the household articles ? Give some examples.
Answer:
Mostly household articles are made up of plastics.
Milk and oil pouches, containers to store pickles and rice, buckets to store water, chairs, water pipes, electric appliances, television, radio and computers, mobile phones, etc. are made of plastic.

Question 21.
What are the properties of thermoplastics and thermosetting plastics ?
Answer:
Thermoplastic will soften when heated and harden when cooled. It is a polymer that turns into a liquid when heated and freezes to a very glassy state when cooled sufficiently. Thermosetting plastics are not remouldable or reheatable. They are poor conductors of heat and electricity. They are fire resistants.

Question 22.
Why polyster is quite suitable for making dress materials ? Name any two types of polyesters and their uses.
Answer:
a) Fabric made from polyester does not wrinkled easily.
b) If remains crisp and it is easy to wash.
c) Terylene is a type of popular polyester.
d) It can be drawn into very fine fibres that can be woven like any other yarn.
e) PET is very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Question 23.
Write some disadvantages of synthetic fibres.
Answer:
a) Synthetic fibres cannot absorb moisture, thus they cannot be used as dress materials during summer.
b) They are dangerous to be worn near fire or heat as they catch fire easily.
c) They cannot be easily ironed.

Question 24.
Explain why plastic containers are favoured for storing food.
Answer:
Three main advantages of using plastic containers for storing food are :
a) They do not react with food items
b) They do not get rusted
c) They are light, strong and durable

Question 25.
Explain why the following are made of thermosetting plastics,
a) saucepan handles
b) electric plugs/switches.
Answer:
Above things are made up of bakelite (thermosetting plastic) because it is
a) bad conductor of heat
b) poor conductor of electricity.

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics 4 Marks Important Questions and Answers

Question 1.
Explain 4R principle for creating ecofriendly environment.
Answer:
The 4R principle involves 1) Reduce 2) Reuse 3) Recycle 4) Recover.

1. Reduce: Reduce the usage of plastic to avoid its negative consequence on environment. Land filling or plastics and burning of plastics in incinerators in the way of disposal of plastics. These have negative consequence on environment. So reduce the usage of plastic whenever it is possible.
2. Reuse: Articles made of plastic is used again and again for its optimum utilization. There by we can decrease the usage of plastics.
3. Recycle: We can recycle the plastic material from broken plastic material that will decrease the production of excess of plastic.
4. Recover: The principle of recover plays major role in plastic waste management. The solid waste should be converted into resources such as electricity, heat, compost and fuel through thermal and biological means.

(OR)

1. Reduce: Try to use less plastic material in our daily life.
2. Reuse: Whenever we need to use plastic material, use the same material again and again don’t go for new one every time.
3. Recycle: Instead of throw away the waste plastic material try to give it the vendor.
4. Recover: Aware the people about establishing “garbage to energy” plant in your area.

Question 2.
Is there any such effort for solid waste management taking place in your village/ town ? How do you appreciate 4R principle?
Answer:
4R Principle is for creating an eco friendly environment.
4R = Reduce, Reuse, Recycle and Recover.
Reduce: Reducing the usage of plastics by reusing them helps the negative conse-quences on environment.
Reuse: When some things made of plastics are not in use to us, we can give them to others who need them. This helps the negative consequence or environment. This is eco friendly.
Recycle: In this process, we can obtain a new substance from the old plastics. Recycling can be used to obtain materials from which the original products were made.
Recover: The solid wastes in which plastics are major should be converted into resources such as electricity, heat, compost and fuel through thermal and biological means.
In these ways 4R principle is eco-friendly.

Question 3.
Explain the differences between the thermoplastics and thermosetting plastics with help of a diagram explaining in terms of arrangements of monomers.
Answer:

Thermoplastics	Thermosetting plastics
Plastics which get deformed easily on heating and can be bent are known as thermoplastics. Ex: PVC, polythene bags, toys, combs, etc.	Plastics which moulded once can’t be softened by heating are called thermo­setting plastics. Ex : Bakelite and melamine.

Explanation:

1. Thermoplastics have linear arrangement of monomers.
2. But thermosetting plastics have cross linked arrangement.
3. The difference in the arrangement of monomers bring the difference in their properties.

Question 4.
Do you know how various synthetic fibres are obtained ?
Answer:
Nylon:
Nylon is a polymer made of chemical units called polyamides which contain carbon, oxygen and nitrogen. Polyamides are melted and forced through a heated spinneret which has very, very tiny holes. The size and shape of the holes changes, the characteristics of the resulting fibre. The fibre solidifies as it cool and can be spun or woven.

Rayon:
The cellulose that was collected from wood or bamboo pulp, is treated with several chemicals.
First sodium hydroxide is added and then carbon disulphide to the cellulose.
The cellulose dissolves in chemicals add to it and gives a syrup called viscose. Viscose is forced through a spinneret, into a solution of dilute sulphuric acid. This gives us silk like threads. The threads are cleaned with soap and dried. This new fibre is called rayon.

Acrylic:
It is made from the combination of coal, air, water, oil and limestone. It is spun by either dry spinning or wet spinning.
In dry spinning the dissolved polymers are extruded into warm air. The fibres solidify by evaporation. In wet spinning the polymers are dissolved and extruded into a bath and then dried.

Question 5.
Can you name the few things made up of i) nylon ii) rayon (iii) acrylic and (iv) polyesters ?
Answer:
The things made from nylon:
Tooth brush bristles, ropes, fishing nets, tents, sarees, stockings and socks, car seat belts, sleeping bags, curtains, etc. are made up of nylon. The things made from rayon: Bed sheets, carpets, home furnishings, sanitary products, diapers and bandages and lints for dressing wounds.
The things made from acrylic: Socks, sportswear and sweaters, craft yarns, upholstery fabrics, carpets, luggage, awnings and vehicle covers.
The things made from Polyester: PET bottles, utensils, films, wires, etc.

Question 6.
Why it is advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen ?
Answer:

1. The synthetic fibres melt on heating.
2. This is actually a disadvantage with synthetic fibres.
3. If the cloth catches fire it can be very disastrous.
4. The fabric melts and sticks to the body of the person wearing it.
5. It is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen.

Question 7.
Classify the material as biodegradable and non-biodegradable.

1. paper
2. wood
3. metals
4. cotton cloth
5. plastic container
6. woolen sweater
7. peels of vegetable and fruit

Answer:

Material	Biodegradable/non-biodegradable
1. paper	Biodegradable
2. wood	Biodegradable
3. metals	Non-biodegradable
4. cotton cloth	Biodegradable
5. plastic container	Non-biodegradable
6. woolen sweater	Biodegradable
7. peels of vegetable and fruit	Biodegradable

Question 8.
Write short notes on the following.
a) Plastic and health care industry b) Plastic cookware c) Teflon d) Fire proof plastic.
Answer:
a) Plastic and health care industry : Plastics find extensive use in the health care industry. Some examples of their use in health care are the packing of tablets, threads used for stitching wounds, syringes, doctor’s gloves, a number of medical instruments, etc.
b) Plastic cookware: Plastic cookware is used in microwave ovens for cooking food. The heating process is different in microwave ovens. The heat cooks the food but does not affect the plastic vessel.
c) Teflon: Teflon is a non-stick plastic used as non-stick coating in cookwares. It is also used as tape for sealing purpose.
d) Fire proof plastics: Although synthetic fibres catches fire easily, it is interesting to know that the fire proof material is made from synthetic plastics.

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics Important Questions and Answers

Question 1.
State government decided to avoid Flexi Banners. Predict the effect of Flexi banners
on environment.
Answer:

1. PVC flexi banners can take several years to decompose in land fills.
2. These flexi banners contain dangerous chemical additives like lead, cadmium which can be toxic to our health as well as animals health.

Question 2.
Write two slogans on solid waste management.
Answer:

1. Convert waste to wealth
   Don’t convert wealth to waste.
2. Recycle waste solid today
   for a better solid future.
3. Reuse, Reduce, Recycle
   The good, The bettel, the best

Question 3.
Draw and explain the diagram of Universal redyeing symbol.
(OR)
Draw “Universal Recycling Symbol”.
Answer:
When the number is omitted from recycling icon then it is known as Universal recycling symbol.

Question 4.
Nylon is a synthetic fibre. Write the advantages and disadvantages of it.
Answer:
Advantages of nylon as fibre:

1. Nylon fibre is strong, elastic and light weight.
2. Cloth made of nylon are lustrous and easy to wash.
3. Nylon does not absorb water.

Disadvantages of nylon as fibre:

1. Synthetic fibres cannot absorb moisture, thus they cannot be used as dress materials during summer.
2. They are dangerous to be worn near fire or heat as they catch fire easily.
3. They cannot be easily ironed.

Question 5.
Though there are so many harmful effects of plastic, we still prefer to use it. What could be its major advantages?
Answer:
Plastics are used in milk and oil pouches, containers to store pickles and rice, buckets to store water, chairs, water pipes, electrical, appliances, television, radio and computers and mobile phones.
Bakelite is used for making handles of various utensils due to its poor conductivity of heat and electricity.

Question 6.
Using an experiment explain how synthetic fibres are stronger than cotton fibres.
Answer:

1. Take an iron stand with a clamp.
2. Take cotton thread and synthetic threads like nylon about 50 cm in length.
3. Tie the cotton thread to the stand, so that it hangs freely from it.
4. At the free and attach a pan, so that a weight can be placed on it.
5. Add weight starting from 10 grams one by one, till the thread breaks down.
6. Note the total weight required to break the thread.
7. Repeat the same activity with synthetic thread also.
8. We can observe that more weights are required to break the synthetic thread than cotton thread.
9. Conclusion: Synthetic threads are stronger than cotton threads.

Question 7.

Answer the following questions.
i) Name the recyclabel material / materials.
ii) Name the thermosetting plastic articles.
iii) Which are thermoplastics but not to be recycled?
iv) Which are recycled but not thermosetting plastics?
Answer:
i) P.E.T bottles
ii) Electric switch, computer keyboard
iii) Polythene bag
iv) P.E.T bottle

Question 8.
Observe the following table.

Answer the following questions.
i. P.E.T is not used in the manufacture of cooker handles. Why?
ii. Which substance is used to manufacture electric switches? Why?
iii. Which is thermo plastic that can not be recycled?
iv. Why we have to ban the polythene covers?
Answer:
i) P.E.T is not used in the manufacture of cooker handles, because it is not a thermosetting plastic.
ii) Bakelite is used to manufacture electric switches, because it is thermosetting plastic.
iii) Polythene and PVC are thermoplastics that cannot be recycled.
iv) Polythene covers cannot be recycled. So, we have to ban the polythene covers.

Question 9.
Based on the smell given in the table identify the fibre and complete the table.

Smell on burning	Name of the fibre
If it smells like burning hair
If it smells like burning paper
If the yarn melts

Answer:

Smell on burning	Name of the fibre
If it smells like burning hair	Wool (or) Silk
If it smells like burning paper	Cotton
If the yarn melts	Polyester (or) nylon

Question 10.
Explain biodegradable and non-biodegradable materials with examples. Include their impact on environment.
Answer:

1. A material which is easily decomposed by natural process is called bio degradable, eg : Peels of fruits, papers, wood, cotton bags, etc.
2. A material which is not decomposed by natural process is called non-bio degradable, eg: Plastic
3. Impact on environment: Slow decomposition causes environmental pollution. The burning process of synthetic materials is also pollute the environment. This pollution causes health problems to the living things.

 

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 6 Sound

AP State Syllabus 8th Class Physical Science Important Questions 6th Lesson Sound

8th Class Physical Science 6th Lesson Sound 1 Mark Important Questions and Answers

Question 1.
What is sound? How does sound produces?
Answer:
Sound is a form of energy. A vibrating body produces sound.

Question 2.
Honeybee produce peculiar sound through their mouth or some other organ used for that purpose?
Answer:
A honeybee can’t make a sound using vocal cords. The buzzing sound that you b*ear from any flying insect is caused by vibration of their wings when flying.

Question 3.
Length of vocal cords in men is nearly 20 mm, in women it is about 5 cir1 less. Whereas in children it is shorter. Can we say that the length of vocal cords plays any role in deciding the quality of sound produced by men, women and children?
Answer:
Yes, we can say that the length of vocal cords decreases then the shrillness °f sound increases.

Question 4.
Pitch of the voices of the following is in ascending order. Lion < adult man < adult woman < child < infant < insect. Can you guess the reason why?
Answer:
The pitch of the voices depend on frequency. As the number of vibrations per second increases the pitch or shrillness increases. So insect produce shrillness due to more frequency of vibration.

Question 5.
Do you find any difference in blowing the whistle and striking the drum?
Answer:
Whistle has more shrillness due to its higher frequency than drum which has less frequency.

Question 6.
Why are some sounds loud?
Answer:
The sounds which have greater amplitude are louder.

Question 7.
Why are some sounds feeble?
Answer:
The sounds which have low amplitude are feeble.

Question 8.
Is there any relation between the intensity of sound and vibrations of the body which produces sound?
Answer:
As amplitude of vibration increases the intensity of sound increases.

Question 9.
How many times is a car horn more powerful than near total silence?
Answer:
It is 10¹¹ times more powerful than a near total silence.

Question 10.
How many times is a jet engine more powerful than a smallest audible sound?
Answer:
It is 10¹² times more powerful than a smallest audible sound.

Question 11.
What is a vibration?
Answer:
The to and fro motion of a body from its mean position is known as vibration.

Question 12.
What is amplitude?
Answer:
The maximum displacement of vibrating body from its mean position is called amplitude.

Question 13.
What are the parts of the speech organ which involved in producing sounds?
Answer:

1. Vocal cords
2. Lips
3. Teeth and tongue
4. Nose and throat

Question 14.
What is a music?
Answer:
Music is a combination of sounds that are produced in an order and pleasant to hear.

Question 15.
What is a noise?
Answer:
The sounds which are not pleasant to hear is called a noise.

Question 16.
What is pitch?
Answer:
The shrillness of a sound is known as pitch.

Question 17.
What is frequency?
Answer:
The number of vibrations per second is called frequency.

Question 18.
What is audible sounds? What is audible range?
Answer:
The sounds that a normal human being can hear is called audible sounds. Frequency of audible sound ranges from 20 cycles / second to 20000 cycles / second.

Question 19.
Do we hear the sounds produced by bats?
Answer:
We cannot hear sounds produced by bats because the sounds produced by bats have frequency more than 20,000 cycles / seconds that is more than audible range.

Question 20.
Does the sound travel if there is no medium?
Answer:
Sound required medium for its propagation. So sound does not travel if there is no medium i.e vacuum.

Question 21.
A bird makes high pitch sound and a lion makes a low pitch roar. Which one produce sound of more frequency?
Answer:
The bird produces sound of more frequency because it has high frequnecy as we already know pitch depends upon frequency.

Question 22.
Why do we produce sounds with different pitches or amplitudes while speaking?
Answer:
The vibration in pitch and amplitude of sound during our speech helps us to communicate with others in form of language.

Question 23.
Lightning and thunder take place in the sky at the same time at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Answer:
The speed of light is more than speed of sound so light travels faster. So we can see lightning first then we can hear thunder.

Question 24.
How intensity of sound related to its unit?
Answer:
The smallest audible sound (nearer to total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful that of total silence is 20 dB. A sound 1000 times more powerful than sound nearer to silence is 30 dB.

Question 25.
How many times is a jet engine more powerful than the whispering sound?
Answer:
The decibel rating of jet engine = 120 dB
The decibel rating of whisper = 20 dB (for practical purpose)
The number of times a jet engine more powerful than a whisper = 10¹⁰ times
{120 – 20 = 100 that is taken as 10¹⁰}

Question 26.
How do you feel when you hear sounds in busy traffic?
Answer:
It is very unpleasant to hear.

Question 27.
How do you feel while listening to songs from a radio?
Answer:
It is very pleasant to hear.

Question 28.
Which of the above sounds are more pleasant to hear?
Answer:
Songs from radio are more pleasant to hear.

Question 29.
What is the unit to measure the sound intensity?
Answer:
Decibel is the unit for measuring the intensity of sound. It is denoted as dB.

8th Class Physical Science 6th Lesson Sound 2 Marks Important Questions and Answers

Question 1.
What is sound pollution? What are the causes of sound pollution?
Answer:
The unwanted sound in our surroundings is called sound pollution.
Causes of sound pollution:

1. Sounds of traffic
2. Sounds by motor bikes and their horns
3. Sounds in construction sites
4. Sounds at industries
5. Sounds at mines
6. Sounds during explosions and bursting of crackers
7. Sounds from mixer/grinder, washing machines and motors, etc.

Question 2.
Write some common sounds and their decibel ratings.
Answer:
Near total silence – 0 dB
A whisper – 15 dB
Normal conversation – 60 dB
A lawn mower – 90 dB
A car horn – 110 dB
A jet engine – 120 dB
A gun shot or fire cracker – 140 dB

Question 3.
How many times is a car horn more powerful than normal conversation?
Answer:
The decibel rating of car horn = 110 dB
The decibel rating of normal conversation = 60 dB
The number of times a car horn more powerful than normal conversation = 10⁵ times
{110 – 60 = 50 which is taken as 10⁵} (The explanation beyond our syllabus. It is based on logarithms)

Question 4.
How can you explain the sound has energy?
Answer:
Sound has energy: Take a plastic bottle and a cell phone.

Cut the top of the bottle so that it looks like a glass. Play songs on the mobile phone in high volume and place it in the bottle. Close the mouth of bottle with a balloon using rubber band so that it covers the bottle as shown in the figure and stretch it tightly so as to behave like a diaphragm. Place some sugar crystals or small sand particles on the balloon diaphragm and observe the movement of particles. Do the same activity after removing the phone from the bottle. Sound has energy

Question 5.
What are the differences between the noise and music? Explain.
Answer:

Noise	Music
1. Sounds which are not pleasant to hear are called Noise.	1. Sounds which are pleasant to hear are called Music.
2. Noise is an irregular combination of sounds.	2. Music is a combination of sounds. Which are produced in order.
3. It is unpleasant to hear.	3. It is pleasant to hear.

Question 6.
Explain the sources which produce sound pollution in your surroundings.
Answer:
Sources of sounds that are produce to sound pollution:

1. Sounds in traffic
2. Sounds by motor vehicles
3. Sounds in construction sites
4. Sounds in industries
5. Sounds in mines
6. Sources of sound pollution like mixer, grinder, washing machines and motors, etc.

Question 7.
What is the effect of humidity on quality of sound propagation? Is there any difference in propagation of sound in air during the summer and winter seasons? Discuss.
Answer:
With increase in humidity, density of air decreases. So with rise in humidity velocity of sound increases.
This is why sound travels in humid air (rainy season or winter) than in dry air (summer) at the same temperature.

Question 8.
Why the voice of men, women and children are different?
Answer:
The vocal cords of men about 20 mm long. In women these cords are about 5 mm shorter in respect to men. Children have very short vocal cords. That is the reason that voice of men, women and children are different.

Question 9.
On which property of vibrations does the loudness of sound depend?
Answer:
The loudness of sound is determined by its amplitude. When the amplitude of a vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.

Question 10.
What are the harmful effects of noise pollution?
Answer:

1. Presence of excessive noise in the surroundings may cause many health related problems.
2. Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorder may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temperory or even permanent deafness.

Question 11.
What is the effect of humidity on quality of sound propagation? Is there any difference in propagation of sound in air during the summer and winter seasons? Discuss.
Answer:
In the winter season the air has fogs and behaves as liquid medium. So, the air moves little faster in it. Whereas in the summer the air is dried and no possibility of droplets. Hence the sound moves slower.
The propagation of sound is Solids > liquids > gases

Question 12.
Define audible sounds and inaudible sounds.
Answer:
Audible sounds:
The sounds that a normal human being can listen are called audible sounds. Frequency range is 20 cycles/sec – 20000 cycles/sec.
Inaudible sounds:
The sounds that a normal human being can’t listen are called inaudible sounds. Frequency range is less than 20 cycles/sec. or greater than 20000 cycles/sec.

8th Class Physical Science 6th Lesson Sound 4 Marks Important Questions and Answers

Question 1.
Describe structure of larynx or voice box.
Answer:
Larynx is the important organ in human body to produce sound. It has two muscular ligaments at the end of wind pipe called vocal cords. They are stretched across voice box, it leads to a narrow slit between them, to allow passage of air.

Vocal cords open during breathing to allow air into lungs. Vocal cords close when we speak.
The air from the lungs presses between them to use vibration and produce sound.

Question 2.
Draw anatomy of the larynx and label its parts.
Answer:

Question 3.
Draw the figures of using three musical instruments in your surroundings.
Answer:

Question 4.
a) Can sound travel in vacuum? Explain.
b) In which medium sound travels much faster and slower? Give some examples.
Answer:
a) Sound can’t travel in vacuum as it needs particles for propagation. As vacuum is empty, it is not possible.
b) Sound travels much faster in solids as the particles in solids are very closely packed, e.g.: Sound travels in train tracks (Railway tracks).
Sound travels much slower in gases as the particles in gases (air) are very loosely packed.
e.g.: Thunder or sound produced from amplifier at a long distance is feeble to hear.

Question 5.
Which object is vibrating when the following sounds are produced?
i) The sound of sitar or veena
ii) The sound of tabla
iii) The buzzing of bee or a mosquito
iv) The sound of a school bell
v) The sound of bursting balloon
vi) The radio
Answer:
i) Strings of sitar or veena vibrate to produce sound.
ii) The skin of the tabla vibrate to produce sound.
iii) Wings of mosquito or a bee vibrate to produce sound.
iv) The disc of the bell when beated with hammer vibrate to produce sound.
v) Air vibrates to produce sound.
vi) In the radio speakers vibrate to produce sound.

Question 6.
On which property of vibrations determines the pitch of the sound? Explain with examples.
Answer:

1. The frequency determines the shrillness or pitch of sound.
2. If the frequency of vibration is higher we say that the sound has a higher pitch.
3. If the frequency of vibration is lower, we say that the sound has a lower pitch. For example, the drum vibrates with a low frequency. Therefore, it produces a low pitched sound:
4. On the other hand, a wristle has a higher frequency, and therefore produces a sound of higher pitch.
5. A bird makes a high pitched sound whereas a lion makes a low pitch roar.

Question 7.
How can the noise pollution be controlled in a residential area?
Answer:

1. The noisy operations must be conducted away from any residential area.
2. Noise producing industries should be set up away from such areas.
3. Use of automobile horns are minimized.
4. T.V and music systems should be run at lower volumes.
5. Plants must be planted along the roads and around buildings to minimize the harmful effects of noise pollution.

Question 8.
What is the audiable range of frequencies for human beings? Explain.
Answer:

1. Sound of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear.
2. Such sounds are called inaudible.
3. On the other side, sound of frequencies more than about 20,000 vibrations per second (20,000 Hz) are also not audible to the human ears.
4. Thus for human ears, the range of audible frequencies is roughly between 20 to 20,000 Hz.

Question 9.
What is eardrum? How does it play an important role in hearings?
Answer:

1. We hear sound through our ears.
2. The shape of the outer part of ear is like a funnel.
3. When sound enters in it, it travels down a canal at the end of which a thin membrane is stritched tightly.
4. It is called the eardrum.
5. It performs an important function.

8th Class Physical Science 6th Lesson Sound Important Questions and Answers

Question 1.
Majority of communication in human beings is through speech. Name the organs which give human beings the ability to talk.
Answer:

1. Vocal cords
2. Lips
3. Teeth and tongue
4. Nose and throat

Question 2.
Why our steps do not produce sound if we walk on a carpet floor?
Answer:
Carpets are soft and as we know soft materials are bad conductors of sound. Thus the
carpet tends to absorb the sound produced. Also when we walk on the carpet the amplitude and vibrations of the floor is reduced leading to a lesser sound.

Question 3.
Sound does NOT travel in vacuum. Explain why.
Answer:

1. Sound energy travels in the form of wave.
2. To produce waves medium is required.
3. Hence, if there is no medium, sound waves cannot form.

Question 4.
Complete the following table.

Vibrating part of instrument	Name of the instrument
Stretched membrane
Stretched string

Answer:

Vibrating part of instrument	Name of the instrument
Stretched membrane	Tabala, Dappu, Mrudangam
Stretched string	Veena, Guitar, Violin

Question 5.
Mention the sounds which are responsible for sound pollution. Suggest four controlling measures of sound pollution.
Answer:
Causes of sound pollution:

1. Sounds of traffic
2. Sounds by motor bikes and their horns
3. Sounds in construction sites
4. Sounds at industries
5. Sounds at mines
6. Sounds during explosions and bursting of crackers
7. Sounds from mixer / grinder, washing machines and motors etc.

The steps to reduce sound pollution :

1. Attach silencers to the bikes and other machines to reduce sound.
2. Manufacture machines that work with lesser noise.
3. During the use of TVs and taperecorders tune down volume of sound.
4. Plant trees to reduce sound pollution.

Question 6.
What is sound pollution? Write effects of sound pollution. Suggest some measures to control sould pollution.
Answer:
The unwanted sound in our surroundings is called sound pollution.
Effects of sound pollution on bio-diversity:

1. The first harmful effect is loss of hearing.
2. It also leads to several health related problems, e.g : Sleeplessness, hypertension, increase in blood pressure, etc.
3. It effects the mental health of people.
4. In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfere with reproduction and navigation and contribute to permanent hearing loss.
5. Noise pollution causes poor quality of crops.
6. Under water animals such as whales and dolphins too experience discomfort due to noise pollution caused by submarines, shipping companies and sonars. Cuttle fish and octopus suffer serious damage from noise pollution.

The steps to reduce sound pollution :

1. Attach silencers to the bikes and other machines to reduce sound.
2. Manufacture machines that work with lesser noise.
3. During the use of TVs and taperecorders tune down volume of sound.
4. Plant trees to reduce sound pollution.

Question 7.
Kushwanth said “Vibrating objects produce sound.” Establish that the given statement is true with relevant example from your surroundings.
Answer:
The statement given by Kushwanth is correct.
That is “vibrating objects produce sound”.
1. Eg: 1) If we ring the bell in the school, sound will produce.
2) If we touch the bell while ringing, vibrations will experience.

2. Eg: 1) We can observe sound coming from the engine of a vehicle.
2) This is due to vibration of the engine.

3. Eg: 1) Musical instruments vibrates and produce sound.
2) If we pull the string of a veena or guitar.
3) It will produce sound.

Question 8.
Based on the below information answer the following questions.

Musical Instrument	Vibrating part producing sounds
Veena	Stretchings string
Tabla	Stretched membrane
Flute	Air Column
Dholak	Stretched membrane
Sitar	Stretching string
Drum	Stretched membrane

a) Name the instruments which have vibrating part like a thin elastic rubber band.
Answer:
Tabla, Dholak, Drum.

b) What are the vibrating particles in the air column?
Answer:
Air particles.

c) What is the difference between Tabla and Sitar in terms of how they produce sound?
Answer:
In Tabla, stretched membrane vibrates and produce sound. Whereas in Sitar stretching string vibrates and produce sound.

d) How to produce different frequencies using a flute?
Answer:
By closing holes of the flute with fingers (or) By changing length of the air column.

Question 9.
Write about the propagation of sound in different media.
Answer:

1. Sound produced by source travels in a medium in the form of waves.
2. Vibrations produced by source of sound travel by particles of medium.
3. In the case of solids, particles of solid substance vibrates and travel along the substance.
4. In the case liquids, molecules of liquids carry the vibrations for sound propagation.
5. In the case of gas, gaseous molecules act as carries of vibrations and allow the sound propagation.

Question 10.
Explain the structure and functions of the ear using a diagram.
(OR)
Describe briefly about structure and functioning of the eardrum.
Answer:
Our ear consists of three sections, the outer ear, the middle ear and the inner ear, Pinna of external ear collects the sound vibrations. They enter into the ear canal. We have learnt that sound travels in the form of vibrations: These vibrations strike the tympanum (eardrum) and make it to vibrate.

The vibrations from the tympanic membrane reach the middle ear (ear ossicles), contains three small bones malleus (hammer shaped), incus (anvil shaped) and stapes (stirrup shaped). They magnify the sound vibrations.
The stapes transmits the vibrations to the membrane of oval window. The oval window has the surface area 1/20th of the ear-drum. By this the vibrations increase 30 to 60 times. The vibrations from the oval window transmit to the cochlea which is the inner part of the ear. The cochlea is filled with fluid which transmits the vibrations. The motion of the vibrations in the cochlea is detected by tiny hairs connected to nerves at this point. The vibrations are transformed into electrical signals and carried by the nerves to the brain where the sensation of the sound is realized.

SCERT AP Board 8th Class Physical Science Solutions 4th Lesson కృత్రిమ దారాలు మరియు ప్లాస్టిక్లు Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science 4th Lesson Questions and Answers కృత్రిమ దారాలు మరియు ప్లాస్టిక్లు

8th Class Physical Science 4th Lesson కృత్రిమ దారాలు మరియు ప్లాస్టిక్లు Textbook Questions and Answers

అభ్యసనాన్ని మెరుగుపరుచుకోండి

ప్రశ్న 1.
కొన్ని దారాలను మాత్రమే మనము కృత్రిమ దారాలు అని ఎందుకంటాం? వివరించండి. (AS1)
జవాబు:

1. నైలాన్, రేయాన్, అక్టోలిక్ మరియు పాలిస్టర్ వంటి కొన్ని దారాలను కృత్రిమ దారాలు అంటారు.
2. పెట్రో రసాయనాలను ఎన్నో రసాయనిక ప్రక్రియలకు గురిచేయడం ద్వారా ఏర్పడే దారాలను కృత్రిమ దారాలు లేదా మానవ నిర్మిత దారాలు అంటారు. కృత్రిమ దారాలు అన్నీ పాలిమర్లు.
3. నైలాన్ అనేది బొగ్గు, నీరు మరియు గాలి నుండి తయారు చేయబడిన కృత్రిమ దారం.
4. రేయాన్ సెల్యులోజ్ తయారుచేయబడ్డ ఒక కృత్రిమ పట్టుదారం.
5. అక్టోలిక్ అనేది నేలబొగ్గు, గాలి, నీరు, నూనె మరియు సున్నపురాయి నుండి తయారయ్యే కృత్రిమ ఉన్ని.

ప్రశ్న 2.
వివిధ పదార్థాలను నిలువ చేయడానికి ప్లాస్టిక్ పాత్రలను వాడడానికి గల కారణాలు చెప్పండి. (AS1)
(లేదా)
ప్లాస్టిక్ లను వాడటం వల్ల అనేక హానికర ప్రభావాలు ఉన్నప్పటికీ మనం ప్లాస్టిక్ లను వినియోగిస్తున్నాము. ఆ ప్లాస్టిక్స్ వలన లాభాలేమిటి ?
జవాబు:

1. ప్లాస్టిక్ నీరు మరియు ఇతర రసాయనాలతో చర్య జరుపదు.
2. పదార్థాలను క్షయం చేయదు.
3. ప్లాస్టిక్ చాలా తేలికైనది, దృఢమైనది, మన్నికైనది.
4. ప్లాస్టిక్ పరిమాణంలోను, విభిన్న రూపాలలోకి మలచగలిగేదిగా ఉంటుంది.
5. ప్లాస్టిక్ వస్తువులు లోహాల కంటే తక్కువ ధరకు లభిస్తాయి.
6. ప్లాస్టికు ఉష్ణబంధక మరియు విద్యుత్ బంధక పదార్థాలు.
7. ప్లాస్టిక్ లను వివిధ రంగులలో తయారుచేసుకోవచ్చును.
   పై కారణాల వలన ప్లాస్టిక్ పాత్రలను వస్తువులను భద్రపరచుకొనేందుకు వాడుతారు.

ప్రశ్న 3.
ఈ క్రింది వానిలో ఏ ఏ పదార్థాలను రీసైక్లింగ్ చేయగలమో, వేటిని చేయలేమో వీడదీయండి. (AS1)
ప్లాస్టిక్ బొమ్మలు, విద్యుత్ స్విచ్లు, ప్లాస్టిక్ కుర్చీలు, బాల్‌ పాయింట్ పెన్నులు, టెలిఫోన్ వస్తువులు, ప్లాస్టిక్ పాత్రలు, కుక్కర్ పిడులు, ప్లాస్టిక్ సీసాలు, పాలిథీన్ సంచులు, పాత్రలు, పళ్ళుతోముకునే బ్రష్ లు, ప్లాస్టిక్ చెప్పులు, ప్లాస్టిక్ ప్లేట్లు, ప్లాస్టిక్ బకెట్లు మొదలగునవి.
జవాబు:

రీసైక్లింగ్ చేయగల పదార్థాలు	రీసైక్లింగ్ చేయలేని పదార్థాలు
ప్లాస్టిక్ బొమ్మలు, ప్లాస్టిక్ కుర్చీలు, ప్లాస్టిక్ పాత్రలు, ప్లాస్టిక్ సీసాలు, ప్లాస్టిక్ చెప్పులు, ప్లాస్టిక్ బకెట్లు	విద్యుత్ స్విచ్ లు, బాల్ పాయింట్ పెన్నులు, టెలిఫోన్ వస్తువులు, కుక్కర్ పిడులు, పళ్ళుతోముకునే  బ్రష్ లు, ప్లాస్టిక్ ప్లేట్లు, పాలిథీన్ సంచులు.

ప్రశ్న 4.
ఎలక్ట్రిక్ స్విచ్ లు థర్మోప్లాస్టిక్ తో తయారుచేస్తే ఏమి జరుగుతుంది? (AS1)
జవాబు:
విద్యుత్ ప్రవాహంలో హెచ్చుతగ్గుల వలన ఎలక్ట్రిక్ స్వి లో ఉష్ణం ఏర్పడుతుంది. థర్మోప్లాస్టిక్ తో తయారుచేసిన ఎలక్ట్రిక్ స్వి లు అయితే ఈ ఉష్ణానికి కరిగిపోతాయి.

ప్రశ్న 5.
థర్మోసెట్టింగ్ ప్లాస్టిక్ కన్నా “ధర్మోప్లాస్టిక్ కు ప్రకృతి నేస్తాలు”. నీవేమి చెబుతావు? ఎందుకు? (AS1)
జవాబు:
థర్మో సెట్టింగ్ ప్లాస్టిక్ ల కన్నా “థర్మోప్లాస్టికు ప్రకృతి నేస్తాలు” ఈ వాక్యాన్ని నేను సమర్థిస్తాను. ఎందుకంటే

1. విరిగిపోయిన, వాడలేని, పాతబడిన థర్మోప్లాస్టిక్ ను వివిధ పద్ధతుల్లో శుభ్రపరచి, రీసైకిల్ చేసి తిరిగి కొత్త వస్తువులను తయారుచేయవచ్చును.
2. థర్మోప్లాస్టిక్ వస్తువులను ప్రతి ఒక్కరూ మళ్లీ మళ్లీ (Reuse) వాడటం ద్వారా పర్యావరణాన్ని కాపాడిన వారమవుతాం.
3. పట్టణాలలోని ఘన వ్యర్థాలలో ఎక్కువ భాగం థర్మోప్లాస్టిక్ వస్తువులే ఉంటాయి. వాటినుండి సేకరించిన వ్యర్థాలను వివిధ పద్ధతుల ద్వారా విద్యుత్, ఉష్ణం, కంపోస్ట్, ఇంధనాల వంటి వివిధ రూపాలలోనికి మార్చి, ఈ వ్యర్థాలను తిరిగి వనరులుగా ఉపయోగిస్తాం.

ప్రశ్న 6.
కింది వాటిని వివరించండి. (AS1)
ఎ) మిశ్రణం
బి) జీవ విచ్ఛిన్నం చెందడం
సి) రీసైక్లింగ్
డి) వియోగం చెందడం
జవాబు:
ఎ) మిశ్రణం :

1. ఏదైనా కృత్రిమ దారాన్ని రెండు లేదా ఎక్కువ ఇతర దారాలతో కలిపే ప్రక్రియను మిశ్రణం అంటారు.
2. టెర్లిన్ ను, నూలుతో మిశ్రణం చేస్తే టెరికాట్ ఏర్పడుతుంది. ఇది సౌకర్యవంతంగా, నలిగిపోనిదిగా ఉంటుంది.
3. టెర్లిన్, ఊన్నితో మిశ్రణం చెందితే టెరిడోల్ ఏర్పడుతుంది.
4. టెర్లిన్, సిల్క్ తో మిశ్రణం చెందితే టెరిసిల్క్ ఏర్పడుతుంది.

బి) జీవ విచ్చిన్నం చెందడం :

1. సహజ ప్రక్రియ ద్వారా పదార్థం సులువుగా వియోగం చెందితే ఆ పదార్థాన్ని జీవ విచ్ఛిన్నం చెందడం అంటారు.
2. పండ్లు, కూరగాయలు, చనిపోయిన జీవులు జీవ విచ్ఛిన్నం చెందుతాయి.

సి) రీసైక్లింగ్ :

1. విరిగిపోయి వాడలేని, పాతబడిన ప్లాస్టిక్ లను వివిధ పద్ధతుల్లో శుభ్రపరచి, తిరిగి ఉపయోగించడానికి అనుకూలంగా కొత్త వస్తువులను తయారుచేయుటను రీసైక్లింగ్ అంటారు.
2. PET (కోడ్-1), PS (కోడ్-6) మరియు HDPE (కోడ్-B) లను రీసైకిల్ చేస్తారు.

డి) వియోగం చెందడం :

1. కొన్ని పదార్థాలు నీరు, సూర్య కాంతి, ఆక్సిజన్ సమక్షంలో ఉంచినపుడు సూక్ష్మభాగాలుగా విడగొట్టబడతాయి. ఈ సూక్ష్మభాగాలు బ్యాక్టీరియా చేత మరల విభజింపబడే ప్రక్రియనే వియోగం చెందడం అంటారు.
2. వియోగం చెందడానికి కావలసిన సమయాన్ని బట్టి ఆ పదార్థం జీవ విచ్ఛినం చెందిందా, చెందలేదా నిర్ణయించవచ్చును.

7. జతపరచండి. (AS1)

1) పాలిస్టర్	ఎ) వంటసామాగ్రి
2) PET	బి) కృత్రిమ పట్టు
3) రేయాన్	సి) ఎక్కువ సంఖ్యలో మోనోమర్లు
4) నైలాన్	డి) ఎలక్ట్రిక్ స్వి చు
5) మెలమిన్	ఇ) చిహ్నం
6) పాలిథీన్	ఎఫ్) ప్రసిద్ధిగాంచిన దుస్తుల సామాగ్రి
7) బేకలైట్	జి) అన్ని దారాలకన్నా దృఢమైనది

జవాబు:

1) పాలిస్టర్	ఎఫ్) ప్రసిద్ధిగాంచిన దుస్తుల సామాగ్రి
2) PET	ఇ) చిహ్నం
3) రేయాన్	బి) కృత్రిమ పట్టు
4) నైలాన్	జి) అన్ని దారాలకన్నా దృఢమైనది
5) మెలమిన్	ఎ) వంటసామాగ్రి
6) పాలిథీన్	సి) ఎక్కువ సంఖ్యలో మోనోమర్లు
7) బేకలైట్	డి) ఎలక్ట్రిక్ స్వి చు

8. ఖాళీలను పూరించండి. (AS1)

i) కృత్రిమ దారాలను …………………….. అని కూడా పిలుస్తాం.
జవాబు:
మానవ నిర్మిత దారాలు

ii) కృత్రిమ దారాలను ………………… పదార్థాల నుండి సంశ్లేషిస్తారు.
జవాబు:
పెట్రోలియం ముడి

iii) కృత్రిమ దారం లాగే ప్లాస్టిక్ కూడా ………
జవాబు:
పాలిమర్

iv) బట్టలపై లేబిళ్లు ……….
ఎ) చట్ట ప్రకారం అవసరం
బి) దారము రకాన్ని గుర్తించడానికి
సి) ఎ, బి లు రెండూ
డి) పైవేవీ కావు
జవాబు:
సి) ఎ, బి లు రెండూ

v) రేయావ్ దీనితో తయారవుతుంది.
ఎ) నేలబొగ్గు
బి) ఆక్సిజన్
సి) నార
డి) సెల్యులోజ్
జవాబు:
డి) సెల్యులోజ్

vi) పట్టుదారము యొక్క నునుపైన తలము కాంతిని శోషిస్తుంది.
ఎ) అవును
బి) కాదు
సి) చెప్పలేము
జవాబు:
ఎ) అవును

ప్రశ్న 9.
రీసైక్లింగ్ ప్రక్రియను మనం ఎక్కడ ఉపయోగిస్తాం? ఇది ఎలా ఉపయోగకరమైనదో ఉదాహరణతో తెల్పండి. (AS1)
జవాబు:
రీసైక్లింగ్ ప్రక్రియను ప్లాస్టిక్ లో మరియు లోహాలలో ఉపయోగిస్తారు.

ఉదాహరణలు :

1. (PET చిహ్నం-1 గలవి) వాడిన లేదా పాడయిన శీతలపానీయాలు, నీటి మరియు పండ్ల రసాల సీసాలు మరియు ట్రేలను రీసైక్లింగ్ చేసి వాహనాల పరికరాలను, ఫ్యూజ్ బాక్స్ లను, బంపరను, తలుపుల ఫ్రేములను, కుర్చీలను మరియు టేబులను తయారు చేస్తారు.
2. HDPE చిహ్నం -2 గలవి) వాడిన లేదా పాడయిన బొమ్మలు, విద్యుత్ బంధక పరికరాలు, పాత్రలు, కుర్చీలు, సీసాలు మొదలగునవి రీసైక్లింగ్ చేసి పెన్నులు, పాటైల్స్, డ్రైనేజి పైపులు మొదలగునవి తయారు చేస్తారు.
3. (PP చిహ్నం-6 గలవి) వాడినవి లేదా పాడయిపోయిన దువ్వెనలు, ఇంటికప్పులు, TV క్యారి కంటైనర్లు, CD కేసులు, డిస్పోజబుల్ ప్లేట్స్, కప్పులు, కోడిగ్రుడ్డు కేసులు మొదలగునవి రీసైక్లింగ్ చేసి విద్యుత్ బంధకాలు, ఎలక్ట్రికల్ స్విలు, గ్రుడ్ల పెట్టెలు, ఫాస్ట్ ఫుడ్ ప్యాకింగ్లు, ఫోమ్ ప్యాకింగ్ న్లు, క్యారి అవుట్ కంటైనర్లు మొదలగునవి తయారు చేస్తారు.

ప్రశ్న 10.
రకరకాల కృత్రిమ దారాలతో తయారుచేసే గృహోపకరణాలు వివరించేటట్లు ఒక పట్టిక తయారు చేయండి. (AS4)
జవాబు:

కృత్రిమ దారం	కృత్రిమ దారాలతో తయారుచేసే గృహోపకరణాలు
1. నైలాన్	బ్రష్ యొక్క కుంచె, తాళ్ళు, చేపలవేటకు వాడే వలలు, గుడారాలు, చీరలు, స్త్రీల మేజోళ్ళు మరియు కాళ్ళకు వేసుకునే చిన్న మేజోళ్ళు (Socks), బెల్టులు, దిండ్లు (Sleeping bags), డోర్ కర్టన్స్, పారాచూట్లు, ఈతదుస్తులు, లో దుస్తులు (Sheer hosiery), తెరచాపలు, గొడుగులకు వాడే గుడ్డ, బట్టలు, కారు టైర్లు మొదలగునవి.
2. రేయాన్	దుస్తులు, దుప్పట్లు, తివాచీలు, లంగోటాలు (Diapers), బ్యాండేజీలు మొదలగునవి.
3. అక్రలిక్	స్వెటర్లు, శాలువాలు, దుప్పట్లు, రగ్గులు, కాళ్ళకు వేసుకొనే మేజోళ్ళు (Socks), క్రీడా దుస్తులు, ప్రయాణ సామగ్రి మరియు వాహనాల కవర్లు మొదలగునవి.
4. పాలిస్టర్	దుస్తులు, చీరలు, బెడ్ షీట్స్, కార్పెట్స్, జాడీలు, సీసాలు, ఫిల్మ్ లు, తీగలు, ప్లాస్టిక్ వస్తువులు, పరికరాలు మొదలగునవి.

ప్రశ్న 11.
థర్మోప్లాస్టిక్ లకు, థర్మోసెట్టింగ్ ప్లాస్టిక్ లకు మోనోమర్ అమరిక విషయంలో ఉండే భేదాలను పట సహాయంతో వివరించండి. (AS5)
జవాబు:

థర్మో ప్లాస్టిక్లు	థర్మోసెట్టింగ్ ప్లాస్టికు
1. వేడి చేసినప్పుడు మృదువుగాను, చల్లబరచినప్పుడు కఠినంగాను మారే ధర్మం గల ప్లాస్టికన్ను థర్మోప్లాస్టిక్ అంటారు.	1. ఒకసారి ఒక రూపంలోనికి మలచి, చల్లబరచిన తర్వాత దాని రూపాన్ని మరలా వేడిచేసినా సరే మార్చలేని ప్లాస్టిక్ ను థర్మోసెట్టింగ్ ప్లాస్టిక్ అంటారు.
2. థర్మోప్లాస్టిక్ లోని మోనోమర్లు రేఖీయ అమరికను కలిగి ఉంటాయి. మోనోమర్ల రేఖీయ అమరిక	2. థర్మోసెట్టింగ్ ప్లాస్టిక్ లోని మోనోమర్లు అడ్డంగా అనుసంధా నించబడిన అమరిక కలిగి ఉంటాయి. మోనోమర్లు అడ్డంగా అనుసంధానించబడిన అమరిక
3. వీటిని వేడి చేసినపుడు ద్రవస్థితిలోనికి, తగినంత చల్లబరిస్తే గాజు స్థితిలోకి ఘనీభవిస్తుంది.	3. వీటిని వేడి చేసినపుడు నల్ల బొగ్గుగా మారుతుంది లేదా మండుతుంది.
4. వీటిని రీసైక్లింగ్ చేయవచ్చును.	4. వీటిని రీసైక్లింగ్ చేయలేము.

ప్రశ్న 12.
“వస్త్ర పరిశ్రమలో కృత్రిమ దారాల పరిచయం వస్త్రధారణ విషయంలో ప్రపంచమంతటా సంస్కృతి, సాంప్రదాయాలకు అతీతంగా విప్లవాత్మక మార్పును తీసుకొచ్చింది”. దీనిని మీరు ఎలా ప్రశంసిస్తారు? (AS6)
జవాబు:
వస్త్ర పరిశ్రమలో సహజ దారాలు సంస్కృతిని, సంప్రదాయాలను తెలియజేసే విధంగా ఉండేవి. సహజ దారాల స్థానంలో వచ్చిన కృత్రిమ దారాలు సహజ దారాలకంటే మెరుగైన లక్షణాలు కలిగి ఉన్నాయి. పాలిస్టర్ అనే కృత్రిమ దారాన్ని కనుగొన్న తరువాత, పాలిస్టర్ దారాలు వస్త్ర పరిశ్రమలో మరియు దుస్తుల సంస్కృతిలో విప్లవాత్మక మార్పులను తెచ్చాయి. ఎందుకంటే ప్లాస్టిక్ వస్త్రము సులభంగా ముడుచుకుపోదు. ఇది ఎక్కువ మన్నికగాను, సులువుగా ఉతుక్కోవడానికి వీలుగాను మరియు తక్కువ ధరలో ఉంటుంది. అందుకే దుస్తులు తయారుచేయడానికి ఈ దారాలు సరిగ్గా సరిపోతాయి. పాలిస్టర్ మిగిలిన దారాల వలె నేయడానికి కూడా వాడవచ్చును. పాలిస్టర్ దారాన్ని సహజదారాలతో కలిపి మిశ్రణం చెందించడం వల్ల సహజ దారాల మరియు కృత్రిమ దారాల లక్షణాలు గల వస్త్రం తయారగును.

వివిధ వృత్తుల వారికి కావలసిన లక్షణాలు గల వస్త్రాలను కృత్రిమ మరియు మిశ్రణం చెందించగా ఏర్పడే వస్త్రాల నుండి పొందవచ్చును. ఈ వస్త్రాలు ప్రపంచమంతటా సంస్కృతి, సంప్రదాయాలకు అతీతంగా విప్లవాత్మక మార్పు తీసుకొచ్చాయని చెప్పవచ్చును.

ప్రశ్న 13.
కృత్రిమ దారాలు మన రోజువారీ జీవితాన్ని ఏ విధంగా మార్చివేసినవి? (AS7)
జవాబు:

1. కృత్రిమ దారాలతో తయారైన గృహోపకరణాల జాబితా చాలా పెద్దది. ఇవన్నీ మన రోజువారీ కృత్యాలతో ముడిపడి ఉంటాయి.
2. కృత్రిమ దారాలు పట్టు వస్త్రాల కంటే ఎక్కువ మెరుపుగల దుస్తులు తయారు చేయడానికి సహాయపడతాయి.
3. నైలాన్ దారం బలంగా ఉండి సాగే గుణాన్ని కలిగి ఉండటం వలన ఈ దుస్తులు త్వరగా చిరిగిపోవు.
4. తక్కువ నీటిని ఉపయోగించి తేలికగా ఉతకవచ్చు.
5. తివాచీలు తయారుచేయడానికి ప్రస్తుతం ఉన్నికి బదులు నైలాన్ వాడుతున్నారు.
6. ఈత కొట్టేటప్పుడు ధరించే దుస్తులు, లోదుస్తులు, గొడుగులు, తెరచాపలు, చేపలు పట్టే వలలు, కార్ల టైర్లు వంటి ఉపయోగకరమైన వస్తువులెన్నో తయారుచేస్తున్నారు.
7. కనుక మన జీవిత విధానం ఈ కృత్రిమ దారాల వినియోగం వలన పూర్తిగా మారిపోయింది.

ప్రశ్న 14.
సుజాత తన తల్లిదండ్రులకు శీతాకాలంలో వేసుకొనే దుస్తులు కొనాలని అనుకొంది. నీవు ఏ రకమైన బట్టలను కొనమని సలహా ఇస్తావు? కారణాలు చెప్పండి. (AS7, AS1))
జవాబు:

1. సుజాత, తన తల్లిదండ్రులకు శీతాకాలంలో వేసుకొనే దుస్తులను కొనాలని అనుకుంది.
2. నేనైతే నిభాకు ఈ క్రింది దుస్తులను కొనమని సలహా ఇస్తాను.
3. సహజమైన ఉన్నితో తయారైన స్వెట్టర్లూ, శాలువాలూ, దుప్పట్లూ మొదలైనవి. కాని ఇవి చాలా ఖరీదైనవి.
4. శీతాకాలంలో వేసుకొనే దుస్తులలో చాలా వాటిని ప్రస్తుతం అక్రలిక్ అనే కృత్రిమ దారంతో తయారుచేస్తున్నారు.
5. ఈ అక్రలిక్ చూడటానికి సహజ ఉన్ని మాదిరిగానే ఉంటుంది.
6. దీనిని కృత్రిమ ఉన్ని అనవచ్చు లేదా నకిలీ ఉన్ని అని కూడా అనవచ్చు.
7. అక్టోలిక ను తడి లేదా పొడి స్పిన్నింగ్ పద్ధతిలో మెలి పెట్టి పురి పెడతారు.
8. దారాలు బాష్పీభవనం ద్వారా ఘనస్థితిని పొందుతాయి.
9. అజోలిక్ తో తయారైన బట్టలు సహజ ఉన్ని బట్టల కన్నా చౌకగా లభిస్తాయి.
10. కనుక నిభా తన తల్లిదండ్రులకు అక్రలిక్ తో చేసిన దుస్తులను కొనడం మంచిది.

ప్రశ్న 15.
వాడిన ప్లాస్టిక్ ను తగిన రీతిలో త్యజించకపోతే (Dispose) వచ్చే అనర్థాలేమిటి? (AS7)
జవాబు:
ప్లాస్టిక్ ను తగిన రీతిలో త్యజించకపోతే వచ్చే అనర్థాలు :

1. ప్లాస్టిక్ కు జీవ విచ్ఛిన్నం చెందనివి కావున ప్లాస్టిక్ వలన భూమి కలుషితం అవుతుంది.
2. వాడి విసిరేసిన పాలిథీన్ సంచులు డ్రైనేజీ వ్యవస్థకు అడ్డుపడి, డ్రైనేజి నీరు రోడ్లపై ప్రవహించుట మరియు కాల్వలో డ్రైనేజి నీరు నిల్వ ఉండడం వల్ల దోమలు పెరిగి వివిధ రోగాలకు కారణమౌతాయి.
3. ఆవులు, మేకలు మొదలగు జంతువులు పాలిథీన్ సంచుల్లోని ఆహార పదార్థాలను తినడం వల్ల జీర్ణవ్యవస్థ, శ్వాసక్రియలు చెడిపోవడం ద్వారా జంతువులు చనిపోతున్నాయి.
4. ప్లాస్టిక్ వ్యర్థాలు చెరువులు, సరస్సులు, నదులు మరియు సముద్రాలలో చేరడం వలన జలచరాలు చనిపోవడం జరుగుతుంది.
5. ప్లాస్టిక్ వ్యర్థాలు భూమిలో చేరడం వలన వర్షం నీరు భూమిలోకి చేరక భూ జలవనరులు క్రమంగా తగ్గిపోతాయి.
6. ప్లాస్టిక్ వ్యర్థాలను మండిస్తే, వాతావరణంలో విషవాయువులు విడుదలవడం వలన వాతావరణ కాలుష్యం ఏర్పడుతుంది.

ప్రశ్న 16.
“ప్లాస్టిక్ విచక్షణారహిత వాడకం జీవ వైవిధ్యానికి ప్రమాదకర హెచ్చరిక” దీనికి సంబంధించి ప్రభుత్వ, ప్రభుత్వేతర సంస్థలు తీసుకొంటున్న చర్యలేమిటి? (AS7)
జవాబు:

1. ప్లాస్టిక్ విచక్షణారహిత వాడకం వలన ప్రకృతిలో కాలుష్యం ఎక్కువైపోతుంది.
2. ఈ వస్తువులు త్వరగా జీవ విచ్ఛిన్నం చెందవు.
3. అందుచేత ప్లాస్టిక్ వాడకాన్ని తగ్గించడానికి “4R” సూత్రాన్ని ప్రభుత్వ, ప్రభుత్వేతర సంస్థలు సుప్రీంకోర్టు ఆదేశాల
   మేరకు విధిగా పాటిస్తున్నాయి.
4. ఈ “4R” లు ఏమంటే
   i) తగ్గించడం (Reduce) : మన నిత్య జీవితంలో ప్లాస్టిక్ ను వీలైనంత తక్కువగా ఉపయోగించాలి.
   ii) మరల ఉపయోగించడం (Reuse) : ప్రతి సారి కొత్త క్యారీ బ్యాగులాంటి వాటిని కొనకుండా వీలైనన్ని ఎక్కువసార్లు మరల మరల తిరిగి వాడాలి.
   iii) తిరిగి ఉపయోగించడానికి అనుకూలంగా తయారు చేయడం (Recycle) : పనికిరాని ప్లాస్టిక్ వస్తువులను వదలివేయకుండ. పాత సామానులు కొనేవాడికి ఇవ్వాలి.
   iv) తిరిగి పొందడం (Recover) : సేకరించిన ప్లాస్టిక్ లాంటి వ్యర్థాలను విద్యుత్, ఉష్ణం వంటి రూపాలలోకి మార్చే పరిశ్రమలు ఏర్పాటు చేసే విధంగా అవగాహన కల్పించాలి.
5. ప్రభుత్వ సంస్థలు, స్థానిక స్వపరిపాలనా సంస్థలు, “మేజిమెంట్ ఆఫ్ వేస్ట్ మెటీరియల్స్” కొరకు ఏర్పడిన స్వచ్ఛంద సంస్థలు ఈ విషయంలో తగిన చర్యలు తీసుకుంటున్నాయి.

పరికరాల జాబితా

పట్టుచీర, నూలు చీర, స్వెటర్, కార్పెట్, బ్రష్, నైలాన్ తాడు, పూసల దండ, పేపర్ క్లిట్ల దండ, వివిధ దారాలు, దారాల ‘మిశ్రణానికి సంబంధించిన లేబుల్స్, రీసైక్లింగ్ చిహ్నాలు గల వస్తువులు, ప్లాస్టిక్ వస్తువుల నమూనాలు, థర్మో ప్లాస్టిక్ వస్తువులు (పివిసి పైపు ముక్క పాలిథీన్ కవర్, బొమ్మలు, దువ్వెన) థర్మోసెట్టింగ్ ప్లాస్టిక్ వస్తువులు (బేకలైట్ స్విచ్, వంటపాత్ర పిడి, మెలమిన్ (కీబోర్డు, ఫైబర్ ప్లేటు) టూత్ బ్రష్, ప్లాస్టిక్ బకెట్, ప్లాస్టిక్ కప్పు, కూరగాయలు, పండ్ల తొక్కలు, తినగా మిగిలిన పదార్థాలు, కాగితం, నూలు బట్ట, ప్లాస్టిక్ సంచి, ఇనుప స్టాండ్, బరువులు వేయడానికి అనువైన పళ్లెములు, బరువులు, లాండ్రీ లేబుల్ కోడ్స్ చార్టు, పట్టుకారు, సారాయి దీపం, రీసైక్లింగ్ చిహ్నాలు చార్టు.

ప్రయత్నించండి

ప్రశ్న 17.
జుట్టు, ఉన్ని, పట్టు, నూలుదారం, ప్లాస్టిక్ ముక్క, స్వెటర్ దారం, తాడుముక్క మొదలగునవి తీసుకొని జాగ్రత్తగా జ్వాల పరీక్ష (Flame test) ను నిర్వహించండి. వాసన, కరిగే విధానాన్ని బట్టి వాటిని సహజ, కృత్రిమ దారాలుగా వర్గీకరించండి. (AS1)
జవాబు:
జ్వా ల పరీక్ష:
ఉద్దేశ్యము :
జ్వాల పరీక్ష ద్వారా నమూనాలను సహజ, కృత్రిమ దారాలుగా వర్గీకరించుట.

కావలసిన పరికరాలు :
పట్టుకారు, సారాయిదీపం, నమూనాలు (జుట్టు, ఉన్ని, పట్టు, కాగితం, నూలుదారం, ప్లాస్టిక్ ముక్క, స్వెటర్ దారం, తాడుముక్క)

పద్ధతి :

1. సారాయి దీపమును తీసుకొని వెలిగించండి.
2. పట్టుకారు సహాయంతో నమూనాలను పట్టుకోండి.
3. సారాయి దీపపు మంటపై నమూనాను పెట్టండి. మండుతున్నప్పుడు వాసన, కరిగే మార్పులను గమనించండి.
4. మిగిలిన నమూనాలతో ఇదే విధంగా మరలా చేయండి. ఫలితాలను పట్టికలో నమోదు చేయండి.

ప్రశ్న 18.
ప్లాస్టిక్ రీసైక్లింగ్ చిహ్నాలు, వాటి పూర్తి పేరు, మరియు దాని సంక్షిప్త నామం, గృహ అవసరాలలో వాటి వినియోగం, రీసైక్లింగ్ అవుతుందా లేదా ఒకవేళ రీసైక్లింగ్ అయితే వాటి నుండి ఏమి తయారు అవుతాయో వీటన్నింటినీ వివరించే ఒక చార్టను తయారుచేయండి. (AS5)
జవాబు:

8th Class Physical Science 4th Lesson కృత్రిమ దారాలు మరియు ప్లాస్టిక్లు Textbook InText Questions and Answers

ఆలోచించండి – చర్చించండి

8th Class Physical Science Textbook Page No. 46

ప్రశ్న 1.
సహజ దారాలకు ప్రత్యామ్నాయాలను గూర్చి మానవులు అన్వేషించడానికి కారణమేమిటి?
జవాబు:

1. సహజ దారాల ఉత్పత్తి ప్రస్తుతం సరిపోవకపోవడం.
2. వీటికి మన్నిక తక్కువ.
3. ఇవి అధిక ఉష్ణం మరియు పీడనాలకు తట్టుకోలేవు.
4. ఇవి ఎక్కువ నీటిని పీల్చుకుంటాయి.
5. వీటితో తయారుచేయబడిన వస్త్రాలు త్వరగా ఆరవు.
6. వీటిని ఎక్కువగా వాష్ చేస్తే పాడవుతాయి. కారణం సంపీడనాలను ఇవి తట్టుకోలేవు.
7. ఇవి ఎక్కువ ధరను కలిగి ఉంటాయి.
8. ఇవి ముడులుగా ఉంటాయి కాబట్టి తప్పకుండా ఇస్త్రీ చేయాలి.
9. ఇవి మెరుపును కలిగి ఉండవు.
10. వీటికి గట్టితనం తక్కువ.
    పై కారణాల వల్ల మానవులు సహజదారాలకు ప్రత్యామ్నాయాలను అన్వేషిస్తున్నారు.

ప్రశ్న 2.
ఏ దారపు వనరులు తరిగిపోకుండా ఉంటాయి? ఎందుకు?
జవాబు:
సహజ దారపు వనరులు తరిగిపోకుండా ఉంటాయి. ఎందుకంటే సహజ దారములు వృక్ష మరియు జంతువుల నుండి తయారవుతాయి.

8th Class Physical Science Textbook Page No. 47

ప్రశ్న 3.
ప్రస్తుత స్థానానికి కృత్రిమ దారాల పరిణామం ఎలా జరిగింది?
జవాబు:
సహజ దారాలు మానవ అవసరాల కన్నా తక్కువ పరిమాణంలో ఉత్పత్తి అవుతున్నాయి. సహజ దారాలకు ప్రత్యామ్నాయంగా కృత్రిమ దారాల కొరకు అన్వేషించవలసిన అవసరం ఏర్పడింది. రెండవ ప్రపంచ యుద్ధ కాలంలో మొట్టమొదట నైలాన్ అనే కృత్రిమ దారాన్ని కనుగొనడం జరిగింది. నైలాన్ దారం బలంగా ఉండి సాగే గుణమున్న తేలికైన పదార్థం. నైలాన్ తో తయారైన బట్టలు మంచి మెరుపును కలిగి ఉంటూ, తేలికగా ఉతుక్కోవడానికి వీలుగా ఉండడం మరియు త్వరగా ఆరే గుణం ఉండడం వల్ల కృత్రిమ దారాల వాడకం పెరిగింది.

8th Class Physical Science Textbook Page No. 49

ప్రశ్న 4.
పారాచూట్ తయారుచేయడానికి నూలుగుడ్డ, నూలు తాడులను వాడితే ఏం జరుగుతుంది?
జవాబు:
నూలుగుడ్డ, నూలు తాడులను పారాచూట్లో వాడితే కింద పడిపోవడం జరుగుతుంది.

కారణాలు :

1. నూలు గుడ్డ, నూలు తాడులు అధిక పీడన, సంపీడనాలను తట్టుకోలేవు.
2. నూలు గుడ్డలో సన్నని రంధ్రాలు ఉండడం వలన గాలి సన్నని రంధ్రాల గుండా సులభంగా ప్రయాణిస్తుంది.
3. నూలు తాడు అధిక బరువులకు తెగిపోతుంది.

ప్రశ్న 5.
పూర్వకాలంలో చేపలు పట్టేవారు నూలు వలలను వాడేవారు. ప్రస్తుతం వారు నైలాన్ వలలను వాడుతున్నారు. నైలాన్ వలల వాడకం వలన లాభాలు ఏమిటి?
జవాబు:

1. నైలాన్ దారాలు అధిక బరువులను తట్టుకోగలవు. కావున వలలు తెగిపోవు.
2. ఇవి గట్టిగా, దృఢంగా ఉండడం వలన చేపలు కొరికినా తెగిపోవు.
3. ఈ దారాలు తడిసినా పాడుకావు.
4. ఇవి అధిక పీడనాన్ని తట్టుకోగలవు.
5. ఇవి నీటిని ఎక్కువగా పీల్చుకోవు. నీటిలో వీటి బరువు ఎక్కువగా ఉండదు.

ప్రశ్న 6.
నైలాన్ చీరలు నూలు చీరల కంటే మెరుగైనవి. మీరు అంగీకరిస్తారా? ఎందుకు?
జవాబు:
నైలాన్ చీరలు నూలు చీరల కంటే మెరుగైనవి. ఎందుకంటే

1. తేలికగా ఉంటాయి.
2. మెరుపును కలిగి ఉంటాయి.
3. ఎక్కువ కాలం మన్నికగా, ఉంటాయి.
4. సులభంగా ఉతకవచ్చును.
5. నీటిని ఎక్కువగా పీల్చవు.
6. త్వరగా ఆరతాయి.
7. ముడుతలు పడవు. ఇస్త్రీ చేయవలసిన అవసరం ఉండదు.
8. కీటకాలు తినవు.
9. పీడన, సంపీడనాలను తట్టుకుంటాయి.
10. తక్కువ ఖరీదుకు లభిస్తాయి.

8th Class Physical Science Textbook Page No. 50

ప్రశ్న 7.
సహజ పట్టుకంటే కృత్రిమ రేయాన్ మెరుగైనదిగా తయారు కావడానికి ఏ లక్షణాలు తోడ్పడతాయి?
జవాబు:

1. రేయాన్ సహజ పట్టు కన్నా చవకైనది.
   చెమటను పీల్చుకొనే స్వభావం ఉండడం.
   స్పర్శకు మృదువుగా మరియు సిల్కీగా ఉండడం.
   కాంతి మరియు మెరుపును కలిగి ఉండడం.
   పై లక్షణాలు సహజ పట్టుకంటే కృత్రిమ రేయాన్ మెరుగైనది అనడానికి తోడ్పడుతున్నాయి.

ప్రశ్న 8.
కృత్రిమ దారముతో తయారైన ఇంటి గడప ముందు కాళ్లు తుడుచుకునే గుడ్డ (Door mat) ను కొనాలని భావిస్తే ఎలాంటి దానితో తయారైన కృత్రిమ దారంను ఎన్నుకుంటావు? ఎందుకు?
జవాబు:
రేయాన్ దారముతో తయారైన కాళ్లు తుడుచుకొను (Door mat) గుడ్డను ఎన్నుకుంటాను. ఎందుకంటే రేయాన్ కి నీరు, తేమను పీల్చుకునే స్వభావం ఉన్నది కనుక.

ప్రశ్న 9.
ఆరోగ్య రక్షణకై వాడే లంగోటీలు (Diapers) మరియు బ్యాండేజ్ లను నైలాన్ తో తయారుచేస్తే ఏమి జరుగుతుంది?
జవాబు:
ఆరోగ్య రక్షణకై వాడే లంగోటీలు మరియు బ్యాండేజ్ లను నైలాన్ తో తయారుచేస్తే నీటిని, చెమటను పీల్చుకొనదు.

8th Class Physical Science Textbook Page No. 51

ప్రశ్న 10.
శీతాకాలంలో ఏ రకపు మిశ్రణం దుస్తులు ఎక్కువ అనుకూలంగా ఉంటాయి? ఎందుకు?
జవాబు:
శీతాకాలంలో టెర్లిన్, ఉన్నితో మిశ్రణం చేసిన టెరిడోల్ దుస్తులు ఎక్కువ అనుకూలంగా ఉంటాయి. ఎందుకంటే ఇది సహజదారాలు మరియు కృత్రిమ దారాల ధర్మాలను కలిగి ఉంటుంది.

ప్రశ్న 11.
సహజ, కృత్రిమ, మిశ్రణం దుస్తులు మనకు లభ్యమవుతున్నాయి కదా! శుభకార్యాలు, పండుగల సమయంలో ఏ దుస్తులు ధరించడానికి ఇష్టపడతారు? ఎందుకు?
జవాబు:
శుభకార్యాలు, పండుగల సమయంలో సహజ దారాలతో తయారైన పట్టు దుస్తులను ధరించడానికి ఇష్టపడతాను. ఎందుకంటే

1. శరీరానికి ఎక్కువ గాలిని తగిలేటట్లు చేస్తాయి.
2. చెమటను పీల్చుకుంటాయి.
3. శరీరానికి చిరాకును కలిగించే రసాయనాలు ఉండవు.
4. వేడికి కరగవు కావున శరీరానికి అంటుకుపోవు.
5. సహజ దారాలు శరీరానికి సౌకర్యంగా ఉంటాయి.

8th Class Physical Science Textbook Page No. 52

ప్రశ్న 12.
సహజ లేదా కృత్రిమ దుస్తులలో వేటిని మీరు ఇష్టపడతారు? ఎందుకు? ఈ రెండింటి మధ్య భేదాలను వ్రాయండి.
జవాబు:
కృత్రిమ దుస్తులు ఇష్టపడతాను. ఎందుకంటే కృత్రిమ దుస్తులు మన్నికైనవి, కాంతిని, మెరుపును కలిగి ఉంటాయి. అన్ని కాలాలకు అణుగుణమైన కృత్రిమ దుస్తులు లభిస్తాయి.

సహజ దుస్తులు	కృత్రిమ దుస్తులు
1) సహజ దారాలు ఎక్కువ ఖరీదైనవి.	1) కృత్రిమ దారాలు చౌకైనవి.
2) సహజ దుస్తులు ముడతలు పడతాయి.	2) కృత్రిమ దుస్తులు ముడతలు పడవు.
3) ఇవి ఎక్కువ నీటిని పీల్చుకుంటాయి.	3) ఇవి తక్కువ నీటిని పీల్చుకుంటాయి.
4) ఇవి త్వరగా ఆరవు.	4) ఇవి త్వరగా ఆరుతాయి.
5) ఇవి మన్నికైనవి కావు.	5) ఇవి మన్నికైనవి.
6) ఇవి కాంతిని, మెరుపును కలిగి ఉండవు.	6) ఇవి కాంతిని, మెరుపును కలిగి ఉంటాయి.

ప్రశ్న 13.
మన దుస్తులను ఇంట్లో ఉతకడానికి, లాండీల్లో డ్రైక్లీనింగ్ చేయడానికి తేడా ఏమిటి?
జవాబు:

ఇంట్లో ఉతకడం	డ్రైక్లీనింగ్
1. దుస్తులను ఉతకడానికి డిటర్జెంట్లు, వాషింగ్ పౌడర్లను ఉపయోగిస్తారు.	డ్రైక్లీనింగ్ లో కర్బన ద్రావణులను ఉపయోగిస్తారు.
2. దుస్తులు అధిక ఉష్ణోగ్రత మరియు ఒత్తిడికి లోనౌతాయి.	2. దుస్తులు అధిక ఒత్తిడికి లోను కావు.
3. రక్తం, గ్రీజు, నూనె, , పెయింట్ల వంటి మరకలు పోవు.	3. రక్తం, గ్రీజు, నూనె, పెయింట్ల వంటి మరకలు పోతాయి.

8th Class Physical Science Textbook Page No. 57

ప్రశ్న 14.
కొన్ని వేపుడు పెనాలకు (Fry Pans) ఆహార పదార్థాలు అంటుకోవు ఎందుకు?
జవాబు:
కొన్ని వేపుడు పెనాలకు ఆహార పదార్థాలు అంటుకోవు. ఎందుకంటే టెఫ్లాతో వేపుడు పెనాలపై పూత పూయబడి ఉంటుంది.

ప్రశ్న 15.
అగ్నిమాపకదళ సిబ్బంది ధరించే దుస్తులు మంటలకు అంటుకోవు. ఎందుకు?
జవాబు:
అగ్నిమాపక దళ సిబ్బంది ధరించే దుస్తులు మంటలకు అంటుకోవు, ఎందుకంటే అవి థర్మోసెట్టింగ్ ప్లాస్టిక్ తో తయారు చేసిన దుస్తులు కాబట్టి.

8th Class Physical Science 4th Lesson కృత్రిమ దారాలు మరియు ప్లాస్టిక్లు Textbook Activities

కృత్యములు

కృత్యం – 1

ప్రశ్న 1.
మీ ఇంటిలో సహజ మరియు కృత్రిమ దారాలతో తయారైన వస్తువులను గుర్తించండి. మీ పాఠశాల, ఇల్లు మరియు మీ పరిసరాలలో ఉన్న వివిధ వస్తువులను, గృహోపకరణాలను గుర్తించి ఆ జాబితాను పట్టికలోని సరియైన గడిలో పొందుపరచండి.
జవాబు:

వనరు	గృహోపకరణాలు
మొక్కల నుండి వచ్చే సహజ దారాలతో తయారయ్యేవి.	నూలు చీర, ఖాదీ బట్టలు, దుప్పట్లు, డోర్ కర్టన్లు, బ్యాండేజీలు మొదలగునవి.
జంతువుల నుండి వచ్చే సహజ దారాలతో తయారయ్యేవి.	పట్టు చీర, స్వెటర్లు, శాలువాలు, డోర్ కర్టన్లు, రగ్గులు మొదలగునవి.
కృత్రిమ దారాలతో తయారయ్యేవి.	బ్రష్ యొక్క కుంచె, తాళ్లు, చేపల వలలు, గుడారాలు, మేజోళ్లు, బెల్ట్ లు, దిండ్లు, తివాచీలు, ఈత దుస్తులు, గొడుగుకు వాడే గుడ్డ, బ్యాండేజీలు, లంగోటీలు మొదలగునవి.

కృత్యం – 2 పూసలు మరియు పేపర్ క్లిక్స్ అమరిక :

ప్రశ్న 2.
కొన్ని పేపర్ క్లిప్ ను తీసుకొని వాటిని పటంలో చూపినట్లు ఒకదానితో ఒకటి కలపండి. క్లిక్స్ అమరిక పద్ధతిని గమనించండి. పూసల దండకు, పేపర్ క్లిక్స్ గొలుసుకు మధ్య ఏమైనా పోలికలు గుర్తు పట్టగలరా?

జవాబు:
పూసల దండలోనూ, పేపర్ క్లిప్ ల గొలుసులోనూ ఒక్కొక్క పేపర్ క్లిప్ పేపర్ క్లి గొలుసు పూస లేక ఒక్కొక్క పేపర్ క్లిప్ రెండవ దానితో కలిసి ఒక పెద్ద గొలుసులాగా ఏర్పడినాయి.

కృత్యం – 3 దారాలను గుర్తించడం – మండించే పరీక్ష :

ప్రశ్న 3.
వివిధ సహజ, కృత్రిమ దారాలను మండించి వాటి లక్షణాలను ఒక పట్టికలో నమోదు చేయండి.
(లేదా)
వివిధ రకాల దారాలను కాల్చినపుడు జరిగే మార్పుల ఆధారంగా దారాలను గుర్తించి పట్టికలో నింపుము.
జవాబు:
పరీక్షించవలసిన వివిధ సహజ, కృత్రిమ దారాలను ఒక్కొక్కటిగా తీసుకొని దాని పురిని, ముడులను విప్పి సారాయి దీపముపై మండించితిని. మండినపుడు పరిశీలించి వాటి లక్షణాలను పట్టికలో వ్రాసితిని.

దారం	లక్షణాలు (మండించినపుడు)
1. నూలు (పత్తి)	వేగంగా మండింది. కాగితం కాలిన వాసన వచ్చింది.
2. ఉన్ని	నెమ్మదిగా మండింది. వెంట్రుకలు కాలిన వాసన వచ్చింది.
3. పట్టు	నెమ్మదిగా మండింది. వెంట్రుకలు కాలిన వాసన వచ్చింది.
4. రేయాన్	వేగంగా మండింది. కాగితం కాలిన వాసన వచ్చింది.
5. నైలాన్	నెమ్మదిగా మండింది. దారము జ్వాలలో కరిగింది.
6. అక్రలిక్	నెమ్మదిగా మండింది. దారము జ్వాలలో కరిగింది.

కృత్యం – 4

ప్రశ్న 4.
నైలాన్ ఎంత బలమైనది ? వివిధ దారాల బలాలను తెలుసుకొను కృత్యమును వివరించండి.
జవాబు:
క్లాంపుతో ఉన్న ఒక ఇనుపస్టాండును తీసుకోండి. 50 సెం. మీ. పొడవున్న నూలు, ఉన్ని, నైలాన్ మరియు పట్టుదారాలను తీసుకోండి. కింది పటంలో చూపిన విధంగా నూలు దారాన్ని కట్టండి. దారం మరొక చివర బరువులు వేయడానికి వీలుగా ఉండే పళ్లెమును వేలాడదీయండి. ఆ పళ్లెములో మొదట 10గ్రా.ల బరువుతో ప్రారంభించి బరువును దారం తెగేంత వరకు పెంచండి. దారం తెగగానే దాని బరువును పట్టికలో నమోదు చేయండి. ఈ విధంగా వివిధ దారాలతో చేసి బరువులను పట్టికలో నమోదు చేయండి. తీసుకున్న అన్ని దారాలు ఒకే పొడవు, దాదాపు ఒకే మందము ఉండేటట్లు చూడండి.

దారపు రకం	దారం తెగిపోవడానికి అవసరమైన భారం సంఖ్య  (గ్రాములలో)
1. నూలు	250
2. ఉన్ని	500
3. పట్టు	550
4. నైలాన్	1200

పై కృత్యంలో దారాల బలాలు పెరిగే క్రమం : నూలు < ఉన్ని < పట్టు < నైలాన్

కృత్యం – 6

ప్రశ్న 5.
ఇచ్చిన సీసా (Bottle) PET సీసా అని ఎలా చెప్పగలవు?

మీ తరగతి స్నేహితుల నుండి వేర్వేరు నీటి సీసాలను సేకరించి వాటిని జాగ్రత్తగా పరిశీలించండి. సీసాల అడుగున త్రిభుజాకారములో ఏదైనా గుర్తు ఉన్నదా? లేదా బ్రాండ్ లేబుల్ స్టిక్కర్ (brand label sticker) పైన ఆ గుర్తు ఉందా? ఆ త్రిభుజంలో ఏ అంకె ఉన్నది? కింది పటంను పరిశీలించండి. చాలా బాటిళ్లకు త్రిభుజాకోరం మధ్యలో 1 అనే అంకె ఉండడం గమనిస్తావు. ఇలా ‘1’ ఉన్నట్లైతే అది PET బాటిల్ అవుతుంది.
రెసినను గుర్తించేందుకు చిహ్నములు :

చిహ్నముల సంఖ్యలు (Code Numbers)

1. పాలీఎథిలీన్ టెరిఫాల్ట్ (PET, PETE)
2. అధిక సాంద్రత గల పాలీ ఎథిలీన్ (HDPE)
3. పాలీవినైల్ క్లోరైడ్ (PVC)
4. అల్ప సాంద్రత గల పాలీ ఎథిలీన్ (LDPE)
5. పాలీ ప్రొపిలీన్ (PP)
6. పాలీ స్టెరీన్ (PS)
7. ఇతరము (1, 2, 3, 4, 5 లేక 6 అని స్పష్టంగా లేని వాటిని లేదా ఒకటి కంటే ఎక్కువ రెసిన్ కలయిక ద్వారా ఏర్పడిన వాటిని ఈ కోడ్తో సూచిస్తారు.)

కృత్యం – 7

ప్రశ్న 6.
వివిధ రకాల వస్తువులను వాటికి గల రీసైక్లింగ్ చిహ్నం ద్వారా గుర్తించండి.
జవాబు:

కృత్యం – 8

ప్రశ్న 7.
ప్లాస్టిక్ రకాలు :
ప్లాస్టిక్ తో తయారైన ఒక PP బాటిల్, మరొక సాధారణమైన బాటిల్ (PET)ను తీసుకొని వేడి నీటిని రెండింటిలో పోయండి.

a) ఏమి మార్పులను గమనించారు?
జవాబు:
సాధారణమైన బాటిల్ ముడుచుకొనిపోయింది. తద్వారా దాని ఆకృతి మారినది.

b) రూపం మారిన సీసా యొక్క చిహ్నము (Code) ను చూడండి.
జవాబు:

c) టప్పర్ వేర్ ప్లాస్టిక్ ఏ రకమైనదో నీవు చెప్పగలవా?
జవాబు:
థర్మోసెట్టింగ్ ప్లాస్టిక్

ప్రయోగశాల కృత్యం

ప్రశ్న 8.
మీకు ఇచ్చిన ప్లాస్టిక్ థర్మో ప్లాస్టిక్లు మరియు థర్మోసెట్టింగ్ ప్లాస్టిక్ లను గుర్తించండి.
(లేదా)
ప్లాస్టిక్ దువ్వెన, పళ్ళుతోముకునే బ్రష్, ప్లాస్టిక్ బకెట్, కుక్కర్ పిడిలు, ఎలక్ట్రిక్ స్విచ్, ప్లాస్టిక్ ప్లేటు, కాఫీ మగ్లను నీకు ఇచ్చినపుడు ఏ కృత్యం చేయడం ద్వారా ఏది థర్మోప్లాస్టిక్, ఏది థర్మో సెట్టింగ్ ప్లాస్టిక్ అని గుర్తించగలవో ఆ కృత్యమును వివరింపుము.
ఉద్దేశము :
జ్వాల పరీక్షను ఉపయోగించి థర్మోప్లాస్టికు మరియు థర్మోసెట్టింగ్ ప్లాస్టిక్ లను గుర్తించుట.

కావలసిన పరికరాలు :
పట్టుకారు, సారాయి దీపం, ఇచ్చిన ప్లాస్టిక్ నమూనాలు.

పద్ధతి :

1. సారాయి దీపమును తీసుకొని దానిని వెలిగించండి.
2. పట్టుకారు సహాయంతో ప్లాస్టిక్ నమూనాను పట్టుకోండి.
3. సారాయి దీపపు మంటపై ఈ నమూనాను పెట్టండి. మండుతున్నప్పుడు జరుగుతున్న మార్పులను గమనించండి.
4. ఈ విధంగా అన్ని నమూనాలను పరీక్షించండి. మీ పరిశీలనలను పట్టికలో నమోదు చేయండి.
5. వేడిచేసినప్పుడు ముడుచుకుపోయే, వంచడానికి వీలయ్యే వాటిని థర్మోప్లాస్టిక్ అంటారు.
6. ఒకసారి మలచిన తర్వాత వేడిచేయుట ద్వారా మృదువుగా మార్చలేకపోతే అటువంటి థర్మోసెట్టింగ్ ప్లాస్టిక్ అని అంటారు.

ప్లాస్టిక్ నమూనా	మెత్తబడడం/కాలిన వాసనతో మండడం/తర్వాత గట్టిపడడం	థర్మోప్లాస్టిక్ థర్మోసెట్టింగ్ ప్లాస్టిక్
1. టూత్ బ్రష్ కుంచె	నెమ్మదిగా మండి మెత్తబడడం, కాలిన వాసనతో మండడం	థర్మోప్లాస్టిక్
2. దువ్వెన	మెత్తబడడం, కాలినవాసనతో మండడం	థర్మోప్లాస్టిక్
3. బకెట్ చిన్నముక్క	మెత్తబడడం, కాలిన వాసనతో మండడం	థర్మోప్లాస్టిక్
4. వంటపాత్ర పిడి	తర్వాత గట్టిపడడం	థర్మోసెట్టింగ్ ప్లాస్టిక్
5. విద్యుత్ స్విచ్	తర్వాత గట్టిపడడం	థర్మోసెట్టింగ్ ప్లాస్టిక్
6. పళ్లెం	తర్వాత గట్టిపడడం	థర్మోసెట్టింగ్ ప్లాస్టిక్
7. కాఫీకప్పు	తర్వాత గట్టిపడడం	థర్మోసెట్టింగ్ ప్లాస్టిక్

కృత్యం – 9 జీవ విచ్ఛిన్నం చెందేవి, జీవ విచ్ఛిన్నం చెందనివి :

ప్రశ్న 9.
ఇచ్చిన పదార్థాలలో జీవ విచ్ఛిన్నం చెందేవి, జీవ విచ్ఛిన్నం చెందనివి గుర్తించి, జీవ విచ్ఛిన్నం చెందుటకు పట్టేకాలాన్ని కనుగొనండి.
జవాబు:
ఒక గుంతను తవ్వి, ఇచ్చిన పదార్థాలను గుంతలో వేయండి. కొన్ని రోజుల తర్వాత గుంతను మరల తవ్వి ఏ పదార్థాలు భూమిలో కలిసిపోయాయో, ఏవి మిగిలిపోయాయో పరిశీలించండి. వివరాలను పట్టికలో వ్రాయండి.

వ్యర్థం పేరు	భూమిలో కలిసిపోవడానికి పట్టేకాలం	మార్పు
1. కూరగాయలు, పండ్ల తొక్కలు	10 – 20 రోజులు	జీవ విచ్ఛిన్నం చెందును.
2. తినగా మిగిలిన పదార్థాలు	10-20 రోజులు	జీవ విచ్ఛిన్నం చెందును.
3. కాగితం	10-30 రోజులు	జీవ విచ్ఛిన్నం చెందును.
4. నూలు బట్ట	2-6 నెలలు	జీవ విచ్ఛిన్నం చెందును.
5. ప్లాస్టిక్ సంచి	100 సం||ల కన్నా ఎక్కువ	జీవ విచ్ఛిన్నం చెందదు.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 7 Coal and Petroleum

AP State Syllabus 8th Class Physical Science Important Questions 7th Lesson Coal and Petroleum

8th Class Physical Science 7th Lesson Coal and Petroleum 1 Mark Important Questions and Answers

Question 1.
What are exhaustible resources? Give examples.
Answer:
The resources which are limited in nature and can be exhausted by human activities are called exhaustible resources, e.g. Coal, petroleum and natural gas.

Question 2.
What are inexhaustible resources? Give examples.
Answer:
The resources which are unlimited in nature and not likely to be exhausted by human activities are called inexhaustible resources, e.g. Solar energy, wind energy, tidal energy.

Question 3.
When and where does petroleum first used?
Answer:
More than 4000 years ago, asphalt (petroleum product) was used in the construction of walls and towers of Babylon. There are also records from ancient China about shallow wells being dug to get petroleum.

Question 4.
What did our ancestors do with petroleum?
Answer:
They mainly used petroleum for their wooden boats and waterproof, as a fuel for lamps and in some traditional remedies.

Question 5.
What is the basic difference between coal and charcoal?
Answer:
Coal used in factories is mined from the earth’s crust. The charcoal is obtained from firewood.

Question 6.
What is meant by fractional distillation?
Answer:
The separation technique used to separate various components of petroleum is called fractional distillation.

Question 7.
What is carbonisation?
Answer:
The slow process of conversion of dead vegetation into coal is called carbonisation.

Question 8.
Why coal, petroleum and natural gas are called fossil fuels?
Answer:
They were formed from the dead remains of living organisms (fossils). So these are called fossil fuels.

Question 9.
What is coke and what are its uses?
Answer:
Coke is a tough, porous and black substance. It is an almost pure form of carbon. Uses:

1. Coke is used in the manufacture of steel.
2. In the extraction of many metals.

Question 10.
Why petroleum is called black gold?
Answer:
Due to its great commercial importance petroleum Is called black gold.

Question 11.
What are alternatives to natural gas? Why do not we are using them?
Answer:
The alternatives for natural gas are coal bed methane and gas hydrates. These are not in commercial production phase due to lack in proper technology.

Question 12.
Can coal, petroleum and natural gas be prepared in the laboratory from dead organisms?
Answer:
No, their formation is very slow process and conditions for their formation cannot be created in the laboratory.

8th Class Physical Science 7th Lesson Coal and Petroleum 2 Marks Important Questions and Answers

Question 1.
How do you obtain various materials we are using in our daily life?
Answer:

Material	Method of obtaining it
Glass	By melting salt with other materials and then, cooling it rapidly
Clay	By mixing the mineral kaolinite with water
Wood	From dried up trees
Plastic	From petrochemicals
Metals	From their respective ores

Question 2.
What is biodiesel? How would you prepare biodiesel? What is its use?
Answer:
Biodiesel is one of the biofuel. Which is not toxic and renewable. It is made from the biological ingredients instead of petroleum or crude oil. Biodiesel usually made from the plant oils or animal fat through a series of chemical reactions.
It is used in diesel engines.

Question 3.
What is coal? Explain the process of formation of coal.
Answer:
Coal is hard and black coloured substance obtained from mines.

The plants in large and dense forests in low lying wet lands got buried under the soil due to natural processes like floods and earthquakes. As more soil deposited over them, the organic matter was compressed. The temperature also rose. As the organic matter sank deeper and deeper, under high temperature and high pressure, the dead plants slowly converted to coal.

Question 4.
What is coal tar and what are its uses?
Answer:
Coal tar: It is a black coloured thick liquid with an unpleasant smell. It is a mixture of about 200 substances.
Uses:
Products obtained from the coal tar are used as starting material for various substances like synthetic dyes, drugs, explosives, perfumes, plastics, paints and roofing material. Naphthaleine balls obtained from coal tar used to repel moths and other insects.

Question 5.
What is coal gas and what are its uses?
Answer:
Coal gas is a gas obtained during the processing of coal to get coke.
Uses:

1. It is used in lighting.
2. It is used as fuel in many industries.

Question 6.
What are petrochemicals? What are the uses of petrochemicals?
Answer: The useful substances which are obtained from petroleum and natural gas are called petrochemicals.
Uses:
They are used in the manufacture of detergents, synthetic fibres (polyester, nylon, acrylic) polythene, etc.

Question 7.
Draw a table showing uses of petrochemicals in various sectors.
Answer:

Agricultural sector	Industrial sector	Domestic and other sectors
Plastic tubes, case, baskets, storing box, cultivation implements, fertilizers.	Cars, motor boats, commu­nication devices, construction materials, paper industry, belt and straps, tyres.	Medical equipments, apparels like clothes, bedding, socks, furniture, paints, washing liquids, road, fibre, cosmetics, medicines, polishing liquids, etc.

Question 8.
Why are coal and petroleum so versatile?
Answer:
Coal consists of mainly carbon while petroleum consists of mixture of compounds called hydrocarbons. These compounds make good starting materials for other compounds based on carbon. Carbon is very versatile and is basis for most of the materials.

Question 9.
Why does the price of petrol go up all the time?
Answer:
The price of anything depends on how much of it is available and how essential it is. Both coal and petroleum are exhaustible resources but we need them, both as fuel and as starting material for synthesising new compounds. Since supply is limited and becoming more expensive as the demand for petrol increase.

Question 10.
What is natural gas ? What are the advantages of CNG as fuel?
Answer: Natural gas is a very important fossil fuel.
CNG: Natural gas is stored under high pressure as compressed natural gas. Advantages of CNG as fuel:

1. CNG is less polluting and it is a cleaner fuel.
2. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes because CNG travels large distances.

Question 11.
Ramu told Rahim that solar energy is inexhaustible resource then what are the questions raised in the mind of Rahim about solar energy?
Answer:

1. If it is inexhaustible resource of energy why don’t we are using it?
2. Whether utilization of solar energy is difficult?
3. Whether sophasticated techniques not available for proper use of solar energy at present?
4. It is costly to use solar energy for producing electric power?

Question 12.
Explain why petroleum is also called as liquid gold.
Answer:

1. They are many useful substances are obtained from petroleum which are called petrochemicals.
2. These are used in the manufacture of detergents, synthetic fibres such as polyester, nylon, acrylic, polythene, etc.
3. Due to great commercial importance petroleum is also called liquid gold.

Question 13.
What will happen if fossil fuels like coal and petroleum are completely exhausted?
Answer:

1. Coal and petroleum are the natural resources which are important resources of energy for us.
2. Coal is used as a fuel as such in homes and in industry, or it is used to generate electricity at thermal power plants.
3. Petroleum products such as petrol and diesel are used as fuels in transport to run scooters, motorcycles, cars, buses, trucks, trains and aeroplanes.
4. Kerosene and LPG obtained from petroleum are used as domestic fuels for cooking food.
5. Since the industrial revolution, we have been using increasing amount of energy. So we need more energy resource.
   So without coal and petroleum products life on the earth is impossible.

Question 14.
Suggest some alternative ways to save the fuel resources. (Or)
What actions are required to meet the future energy needs?
Answer:

1. Do not waste fuel for unnecessary activities.
2. The energy should be properly utilized and the wastage should be minimized.
3. Usage of bicycle in place of motor vehicles for small distances.
4. Using road transport vehicles for travelling larger distances which will minimize fuel consumption.
5. The engine of a vehicle thoroughly serviced in order to minimize fuel consumption.
6. Alternative sources like solar energy, wind energy, tidal energy are more utilized.

Question 15.
Burning fuels releases carbon dioxide , a green house gas, which causes climate changes and leads to global warming. Collect information about this through newspapers, magazines, etc. and prepare report.
Answer:
i) Drastic increase in the emission of CO₂ within last 30 years caused by burning of fossil fuels has been identified as the major reason for the change of temperature in atmosphere.
ii) Carbon dioxide in the atmosphere traps the reflect sunlight and re-emitt towards earth which is causing increase of earth temperature what we call as global warming.

Question 16.
Describe characteristics and uses of coke.
Answer:

1. It is tough, porous and black substance.
2. It is almost pure form of carbon.
3. Coke is obtained by heating soft coal in the absence or little supply of air.
4. It is used in the manufacture of steel and extraction of many metals.

8th Class Physical Science 7th Lesson Coal and Petroleum 4 Marks Important Questions and Answers

Question 1.
Is petroleum exhaustible? Explain.
Answer:

1. If we see the history of petroleum production, from 1859 to 1969, the total production of oil was 227 billion barrels.
2. 50% of this total was produced during the first 100 years, while the next 50% was extracted in just ten years.
3. Today our consumption rate of oil is far excess that of the rate of its formation.
4. Earth take more than one thousand years to form the oil that we consume in one day.
5. By about 2015, we would have consumed half of the total reserves of the oil.
6. It would become more and more difficult to extract oil in future.
   So petroleum is exhaustible.

Question 2.
Draw a diagram showing existence of various fuels like natural gas, petroleum in earth crust.
Answer:

Question 3.
Collect information about places where we get coal, petroleum and natural gas in India and mark the places on outline map of India.
Answer:
Coal: Jharia, Chandrapura, Bokaro, Giridih (Jarkhand), Ranigunj and Asansol (West Bengal), Singrauli (M.P.), Korba (Chhattisgarh), Singareni (A.P.) : Talcher and Rampur Himgir (Odisa) and Chand coal field (Maharashtra).
Petroleum : Digboi, Hugrijan, Moran, Naharkatiya, Sibsagar, Rudrasagar and Badarpur (Asom), Bombay High (Maharashtra), Ankleshwar, Kosamba, Kalol, Mehsana, Navagam and Dholka (Gujarat), Krishna and Godavari river basins (A.P.)
Natural gas: Cambay and Ankleshwar fields (Gujarat) and Bombay High (Maharashtra), Coastal Andhra Pradesh.

8th Class Physical Science 7th Lesson Coal and Petroleum Important Questions and Answers

Question 1.
Write any two uses of petrochemicals in our daily life.
Answer:
Uses: They are used in the manufacture of detergents, synthetic fibres (polyester, nylon, acrylic) polythene, etc.

Question 2.
It is necessary to save the energy resources like petroleum and natural gas. Write a slogan about this to create awareness among people.
Answer:

1. ‘Save petrol and save future’.
2. ‘Save fuel and save earth’.

Question 3.
Petroleum is a complex mixture. Write the technique to separate its components.
Answer:
The technique to separate petroleum components is ‘fractional distillation’.

Question 4.
Write any two uses of Activated Carbon in our daily life.
Answer:
Uses of Activated Carbon:

1. Activated Carbon is used to purify liquids.
2. It is used to treat many types of oral poisonings.

Question 5.
Assume that you are a driver, what measures do you take to save petrol?
Answer:
Engine must be stopped in the traffic signals or in heavy traffic.

Question 6.
The following table shows the total power shortage percentage in India from 1994-1997. Observe the data and give the answers to the following questions.
i. In which year the shortage percentage of power is least?
ii. Between which two years the shortage percentage difference is more?
iii. In which year the shortage percentage of power is maximum?
iv. Make a comment on shortage percentage of power between 1994-95.
Answer:
i. 1995
ii. Between 1996 and 1997
iii. 1997
iv. Shortage percentage is decreased by 0.3 in between 1994 – 95.