ENERGY

1. Define energy with it's unit.
- The capacity of doing work is called energy. It's unit is Joule and CGS unit is calorie.

2. State law of conservation of energy.
- Law of conservation of energy states that, energy can neither be created nor be destroyed but it can be transformed from one form to another.''

3. Define primary sources of energy with it's types.
- Primary sources of energy can be defined as the source of energy which are utilize in the form of natural availability. It's types are:
a. Non-renewable sources of energy: The sources of energy that cannot be renewed time and again and take a very long time to form once they finish are called non-renewable sources of energy. For example, coal, mineral oil, natural gas etc.
b. Renewable sources of energy: The sources of energy that can be renewed time and again and do not take a very long time to form once they finish are called renewable sources of energy. For example, solar energy, bio mass, hydro electricity etc.

4. Why is the sun called ultimate source of energy?
- The sun is called the ultimate sources of energy because it is the prime or major source of energy and solar energy is stored in all sources of energy, directly or indirectly.

5. What are the conditions required for nuclear reaction in the sun?
- The necessary conditions required for nuclear energy in the sun are:
a. Presence of high temperature in the sun.
b. Presence of abundant amount of  hydrogen gas in the sun.
c. Presence of high pressure in the sun.

6. What are the types of nuclear reactions?
- The types of reactions are as follows:
a. Nuclear fission reaction: The process in which a heavy nucleus of a radioactive element breaks down into two or more lighter nuclei is called a nuclear fission reactions. It can be controlled.
b. Nuclear fusion reaction: The process in which two or more than two lighter nuclei fuse together together to form a single heavy nucleus  is called a nuclear fusion reaction. It cannot be controlled.

7. Define nuclear fuel.
- The radioactive material which is used in the process of nuclear reaction is called nuclear fuel.

8. What are the three isotopes of hydrogen?
- The three isotopes of hydrogen are Protium, Deuterium(Heavy hydrogen) and Tritium(isotope of hydrogen).

9. Define fossil fuels.
- The fuels obtained from the dead remains of plants and animals that were buried in the earth's crust millions of year ago are known as fossil fuel.

10. Define coal.
- The hard and black rock which contains carbon is called coal.

11. What are the benefits of coal and mineral oil?
-  The benefits of coal and mineral oils are as follows:
a. Coal and mineral oil have low cost and can easily be transported.
b. Coal and mineral oil are more abundant in comparison to other types of fuels.
c. They give abundant heat after combustion.