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.