1. Fill in each blank with the appropriate term from the brackets.
(a) A bucketful of water is to be drawn from a well. Work will be done when a force is applied to do this, because there will be a displacement of water. (displacement, work, force)
(b) If a ball is dropped on the sloping roof of a house, it acquires motion and falls on the ground. That is, transformation of potential energy into kinetic energy takes place. (kinetic, potential, motion)
(c) You might have seen some beautiful fireworks during Diwali. It is an example of transformation of chemical energy into light energy. (light, atom, chemical, solar)
(d) The solar cooker is an application of the heat energy of the sun, while solar cells, solar lamps are applications of the light energy of the sun. (light, chemical, heat)
(e) One labourer carried four pans of road metal through a distance of 100 metres. If he carries two pans of road metal through a 200 metre distance equal work will be done. (equal, more, less)
(f) The capacity that an object has for doing work is called energy. (energy, displacement, force)
2. Match the pairs.
|Group ‘A’||Group ‘B’|
|(1) Rolling object||(a) Heat energy|
|(2) Food||(b) Atomic energy|
|(3) Stretched bow||(c) Kinetic energy|
|(4) Sunlight||(d) Potential energy|
|(5) Uranium||(e) Chemical energy|
Ans: 1 – c; 2 – e; 3 – d; 4 – a; 5 – b
3. Can you tell ?
(a) When can we say that displacement has taken place?
Ans. We can say that displacement has taken place when the position of an object has changed.
(b) What should be taken into account for measuring work?
Ans. For measuring the work, both the force and the displacement must be considered.
(c) What are the various forms of energy?
Ans. The various forms of energy are mechanical energy, heat energy, light energy, sound energy, chemical energy and electrical energy.
(d) Describe one natural chain of transformation of energy.
Ans. Electrical energy is used in our houses for various purposes. It is transformed into light energy on lighting a bulb, into kinetic energy on starting a fan, into sound energy while playing a music system, and into heat energy in an oven.
(e) Why should we save energy?
Ans. Due to the increasing population and increasing usage of energy resources, there is a danger that the limited reserves of coal, petrol, diesel, crude oil and natural gas will get exhausted. We cannot replenish these resources. Therefore we should save energy.
(f) What is ‘green energy’?
Ans. The energy resources which do not produce smoke and carbon gases such as carbon dioxide or carbon monoxide are called ‘Green energy resources’.
(g) What are the non-conventional energy resources?
Ans. The energy resources that have not been used traditionally, are inexhaustible and continuous and can be used in various forms again and again are called non-conventional energy resources.
(h) Which forms of energy from the sun are used in solar energy devices?
Ans. In the solar cooker, solar water heater and solar drier, heat energy obtained from the sun is utilized to cook food, heat water and to dry grain. In a solar cell, electrical energy can be obtained from solar energy.
(i) Why should we maximise the use of non-conventional energy resources?
Ans. Non-conventional energy resources or renewable energy resources are inexhaustible and continuous and can be used in various forms again and again. They also do not produce smoke and carbon gases such as carbon dioxide or carbon monoxide. Therefore we should maximise the use of non-conventional energy resources.
4. Who is the odd-one-out ?
(1) Diesel, crude oil, natural gas, wind
Ans. (1) Wind is the odd one out as it is a non-conventional energy resource and the rest are conventional energy resource.
(2) A running car, hauling a log, a book kept on a table, picking up the school bag.
Ans. A book kept on a table is the odd one out as no work is done and in the rest, work is being done.
(3) Sunlight, wind, waves, petrol
Ans. Petrol is the odd one out as it is a conventional energy resource and the rest are non-conventional energy resource.
(4) Leaving the fan on in a vacant room, leaving the TV on while working, using AC during winter, putting off the light when going out.
Ans. Putting off the light when going out is the odd one out as it is one of the measures of saving energy, the rest are wastage of energy.
5 Find out the types of energy from the following puzzle.
Extra Textual questions
Use your brain power !
Is a displacement possible without a force ?
Ans. Displacement is not possible without force.
If a force is applied with both the hands on a wall, will there be a displacement?
Ans. No, there will not be any displacement.
If no displacement occurs on applying a force, what does it indicate?
Ans. If no displacement occurs on applying a force, what does it indicates that no work was done.
When did you feel that more work was done ?
Ans. More work is done for the same displacement, when more force is applied to do the work. If the same force is applied for more displacement, more work is done by the force.
Run around the ground with your friends. Can your friends run as many rounds as you can?
Ans. My friends will complete either more or less rounds than the number of rounds I complete.
Do all the friends have the same capacity for running?
Ans. Some will get tired on completing two rounds, while others will get tired on completing three or four rounds. That is to say, each one’s capacity to complete rounds is not the same.
Why do you get hungry after physical exercise?
Ans. After a rigorous physical exercise, our body has utilized all the energy. Therefore we feel hungry after physical exercise.
From where does our body get energy?
Ans. Our body gets energy from the food we eat.
Why do we get tired?
Ans. When we have exhausted our capacity to do work, we get tired.
What will happen if the rubber band is released after stretching it and a stone is held in the rubber of a catapult, the rubber is stretched and released?
Ans. In the above examples we see that when the rubber band is released after stretching it, comes back to its original position. So also when the rubber of a catapult is stretched and released, it comes back to the original state and the stone flies off.
In the game of marbles, from where does one marble get energy to set another marble in motion?
Ans. In the game of marbles, the first marble gets the energy from its motion which is called kinetic energy, to set another marble in motion.
While playing carrom, from where does the striker get the energy to make the pieces move?
Ans. While playing carrom, the striker gets the energy from its motion, which is called kinetic energy to make the other pieces move.
1. Generally, grapes which appear in the market during December and January are sour. However, in March-April the grapes are sweet. Why is this so?
2. How does a picture appear on the screen of a TV, mobile, laptop and a cinema theatre?
Fill in the blanks:
1. When an object is displaced by applying a force on it, work is said to be done.
2. For measuring the work, both the force and the displacement must be considered.
3. The capacity to do work is called energy.
4. Work and energy are both measured in the unit named Joule in S.I. (System International) units.
5. The energy used for doing mechanical work is called mechanical energy.
6. There are two types of mechanical energy, namely, potential energy and kinetic energy.
7. The energy which is stored in an object due to a specific state or position of that object is called potential energy.
8. The energy obtained from motion is called kinetic energy.
9. Sunlight contains heat energy.
10. Heat is measured in the unit Calorie.
11. The energy obtained through chemical action is called chemical energy.
12. Electrical energy is used in our houses for various purposes. It is transformed into light energy on lighting a bulb, into kinetic energy on starting a fan, into sound energy while playing a music system, and into heat energy in an oven.
13. The sun is the most important source of all energy.
14. The energy resources which man has been using for centuries are called conventional energy sources.
15. Conventional energy resources include coal and fossil fuels such as petrol, diesel and natural gas.
16. Non-conventional energy resources or renewable energy resources are inexhaustible and continuous and can be used in various forms again and again.
17. The Koyna project in Maharashtra is a well-known hydel project.
18. Saving energy is as good as generating energy.
19. The energy resources which do not produce smoke and carbon gases such as carbon dioxide or carbon monoxide are called Green energy resources.
20. Energy resources are of two kinds: conventional (non-renewable) and non-conventional (renewable) energy resources.