What is meant by a source of energy?

The raw materials that provide the requisite amount of energy to perform various functions of life are called sources of energy.

For example:
(i) We need heat energy to cook food.
The various sources are: Fuels, wood, coal, kerosene, cooking gas etc.
(ii) We need energy for our transport.
The various sources are: Petrol, diesel.
(iii) We need energy to light bulbs, tubes, to run radio, television and other power appliances.
The source is electricity.
(iv) Production in factories and agriculture also need energy.
The source is diesel and electricity.

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List any four sources of energy which are selected for use for a given activity. 

1. Energy to run a cycle
2. Energy to run a car
3. Energy to cook food 
4. Energy to work on 


Four sources of energy used in the activity is:

1. Energy of muscles 
2. Chemical energy of petrol or diesel
3. Chemical energy of gas or kerosene
4. Electrical energy obtained from potential energy. Electrical appliances of water, chemical energy of fuels etc. 

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Name the source of energy in sun and stars.


Nuclear fusion is the source of energy in sun and stars. 
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What are the characteristics of a good source of energy?


Characteristics of a good sources of energy are:

(i) it should give an adequate amount of net energy or work per unit volume or mass,
(ii) it must be convenient to use so as to give energy at a steady rate,
(iii) it must be easy to store and transport,
(iv) it must be economical, and
v) it must be easily accessible. 

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Energy can neither be created nor destroyed. Then why is there so much fuss about energy crisis?

It is true that energy can neither be created no be destroyed but, is converted to one form of energy to another. The fuss because of the fact that, energy in the usable form is dissipated to the surroundings in the less usable form.

For instance, when a candle burns it gives heat, light and other substances but the heat, light and these other substances cannot be put together to give wax to be used again. 
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