Energy Stored in Capacitor

The charging of a capacitor can be visualized as if some external agent, say a battery, pulls electrons from the positive plate of a capacitor and transfers them to the negative plate. Some work is done in transferring this charge, which is stored in the capacitor in the form of electrostatic potential energy. This energy is obtained from the battery (stored as chemical energy). When this capacitor is discharged through a resistor, this energy is released in the form of heat.

The charging takes place slowly. The initial potential difference between the capacitor plates is zero and the final potential difference is V. The average potential difference during the entire process of charging is

(0+V)/2 = V/2

= q/2C

The work done during charging is given by

W = Charge × potential difference

= q × q/2C = q²/2C

Potential energy is given by

U = ½qV = ½q²/C = ½CV²

This energy is stored in the electric field between the plates. The stored energy is directly proportional to the capacitance. It also increases as potential difference increases. However, every capacitor can store only a limited amount of energy. An automatic discharge will take place when the potential difference becomes more than its threshold value.