SOURCES OF ENERGY
One form of energy can be converted to another. E.g.
o When a plate hits the ground, potential energy is converted to sound energy.
o In a burning candle, chemical energy is converted to heat energy and light energy.
But these energy forms cannot be reversed again to the previous forms.
When hot water is kept in room temperature, the heat energy is lost to the environment. But this lost energy cannot be re-collected to heat the water again.
Dissipated usable energy cannot be used again.
Various sources of energy are used for doing work.
Muscular energy to carry out physical work, electrical energy for running various appliances, chemical energy for cooking food or running a vehicle all come from some sources.
Various fuels for cooking include Electricity, LPG, Wood, Coal, solar cooker, etc.
A good fuel is easily available, efficient, cheap, clean, and easy to use producing no or least pollutants. E.g. In home, LPG & electricity are preferred as they are highly efficient, smokeless, easily available and easy to use.
Selection of fuels also depends on the work to be done and the amount of energy needed.
Advantages of a good source of energy:
o Do huge work per unit volume or mass.
o Easily accessible.
o Easy to store and transport.