CBSE Class 9 Answered

One important property of energy is its ability to change from one form to another form. For example, chemical energy from fossil fuels (coal, oil and natural gas) can be converted into heat energy when burned. The heat energy may be converted into kinetic energy in a gas turbine and finally into electrical energy by a generator. The electric energy may subsequently be converted into light, sound or kinetic energy in our homes through various household appliances.

During any energy conversion, the amount of energy input is the same as the energy output. This concept is known as the law of conservation of energy. This law states: Energy cannot be created nor destroyed but can be transformed from one form to another. Thus, the total energy of an isolated system is always constant and when energy of one form is expended an equal amount of energy in another form is produced.