Capacitor Energy

Formula

Description

The energy stored in a capacitor is proportional to the capacitance and the square of the voltage across it. The quadratic voltage relationship means that doubling the voltage quadruples the stored energy, which is why high-voltage capacitors can be extremely dangerous even at small capacitance values. This energy is stored in the electric field between the capacitor plates. Supercapacitors exploit this principle with very high capacitance values (farads rather than microfarads) to serve as short-term energy storage devices that bridge the gap between batteries and conventional capacitors.

Variables

• E — Energy in joules (J)
• C — Capacitance in farads (F)
• V — Voltage across the capacitor (V)

Practical Notes

A fully charged camera flash capacitor (typically 300µF at 300V) stores about 13.5 joules, enough to be lethal. Always discharge capacitors safely before working on circuits. The energy can also be expressed as E = Q²/(2C) or E = QV/2.