Capacitance

Work is performed to accumulate charge in a capacitor. Each additional electron stored must overcome the repelling force caused by the charge previously stored. Energy storage increases as the square of the voltage across a capacitor. This often considerable energy can be used later.

Capacitors used as energy reservoirs can deliver powerful pulses of energy. A capacitor can discharge quickly then slowly recharge until the next power demand. The power source needs only to be large enough to supply the average energy. Inexpensive audio amplifiers often use large capacitors to provide high power peaks required by occasional loud sounds. Quiet intervals allow the capacitor to recharge before the next power burst.