CHAPTER: Energy Class 7

1. What is energy? Write the S.I. Unit of it.

Ans: The ability to do work for a substance is called energy. S.I. Unit - joule ( J ).

2. What is the relation between calories and joule?

Ans: 1 calorie = 4.2 joule ( 4.186 )

3. How many types of mechanical energy?

Ans: Two types of mechanical energy.

        i) Kinetic energy (1/2 mv² )

       ii) Potential energy ( mgh )

               Potential energy is also two types.

               a) Elastic potential energy ( stretched bow )

               b) Gravitational potential energy ( water tank on height )

4. How many types of energy?

Ans: i) Mechanical energy

        ii) Heat energy

       iii) Sound energy

       iv) Electrical energy

        v) Light energy

       vi) Geothermal energy, etc.

5. Write the law of conservation of energy.

Ans: Energy can not be created or destroyed, it is converted from one form to another.

6. How freely falling body follow the conservation of energy?

Ans: A body falls from point X. Total energy on point X - Kinetic energy is Zero but Potential energy is maximum. So total energy is e + 0 = e.

  Point Y, if the total height is (a ), so the substance falls from X and covers a / 2 distance, and Potential energy is converted into Kinetic energy. So total energy on point Y = e / 2 + e / 2 = e.                                                                                             

  Point Z, the substance falls and touches the ground. Before touching the ground Kinetic energy is maximum. So total energy on point Z is 0 + e = e.

  In all the points total energy is the same ( e ). So, in this case, the law of conservation of energy follows.

7. What happens when the bow and arrow band is stretched?

Ans: After stretching the bow the potential energy stored in the bow band after removing the stretch bow potential energy is converted into kinetic energy and the arrow goes forward.

8. Give some examples of energy conversion.

Ans: i) Microphone - Sound energy to Electric energy.

        ii) Loudspeaker - Electric energy to Sound energy.

       iii) Solar cell - Solar energy to Electric energy.

       iv) Battery - Chemical energy to Electric energy.

        v) Electromagnet - Electrical energy to Magnetic energy.

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