Energy used is dissipated in less usable form. The energy used is consumed and cannot be used again.
Example: Burning of candle → light + heat but the product cannot produce chemical energy.
Detailed Answer:
The law of conservation of energy states that energy can neither be created nor be destroyed. But, it can only be converted from one form to another. Despite this fact, the world is facing energy crisis. The reason behind it is that energy is converted into non-usable forms.
Fossil fuels like coal, petroleum etc. are the sources of energy which have accumulated in nature over a long time and cannot be replaced. We should worry about such sources because these sources of energy are getting depleted and sooner or late, will no longer be available to us.
