Power is defined as the energy that is consumed or converted in a certain amount of time. In a simple electrical circuit, the power is found by multiplying the voltage and current. An electric current is the movement of charged particles measured in amperes and the voltage of the force driving them. Current that flows in one direction only, such as the current in a battery-powered flashlight, is called direct current. Current that flows back and forth, reversing direction again and again, such as household current, is called alternating current. Household electricity bills are computed on the basis of how many thousand-watt hours (kWh) of energy are consumed over a certain period of time. Today's home consumes, on average, between twelve hundred and two thousand kWh per month.

Most of the world's electric power is generated in steam plants. In a steam turbine generator, fossil fuel...