Capacitor Energy

A capacitor stores energy by separating positive and negative charge on its plates, creating an electric field between them. The factor of 1/2 appears because the voltage is not constant while the capacitor charges; the first bit of charge is added when the voltage is low, and later bits are added against a higher voltage, so the average charging voltage is V/2. That is why the stored energy depends on both the capacitance and the square of the final voltage.

Use this formula when you need the energy held in a charged capacitor, such as in flash units, power supplies, timing circuits, or safety calculations for high-voltage capacitors. It is also useful when comparing how much energy changes if capacitance or voltage changes.

• Using the capacitance value in microfarads without converting to farads
• Forgetting to square the voltage
• Leaving out the 1/2 factor from the energy formula