Capacitor Energy

This formula gives the electrical potential energy a capacitor stores when it has charge separated across its plates. It comes from the work needed to move charge onto the capacitor: as more charge builds up, the voltage rises, so the average voltage during charging is half the final voltage, which leads to the factor of 1/2. The stored energy depends on both how much charge the capacitor can hold (capacitance) and how high the voltage is, with voltage having a particularly strong effect because the energy scales with V^2.

Use this when you need to find how much energy is stored in a capacitor in a circuit, such as in flash units, power backup circuits, timing circuits, or energy-storage calculations. It is also useful when comparing different capacitor-voltage combinations to see which stores more energy.

• Using capacitance in microfarads without converting to farads
• Forgetting to square the voltage term
• Mixing up capacitor energy with power, which is measured in watts rather than joules