19.2 Energy stored in a capacitor

Energy stored in a capacitor is electric potential energy associated with separated charge and the electric field between conductors.

Charging requires work against the growing potential difference; discharging transfers this energy to other stores or radiation.

A camera flash capacitor releases stored electric energy rapidly through a lamp circuit.

The dielectric does not create energy; it changes capacitance and the energy relation for a given Q or V.

For a linear capacitor, stored energy W=½QV=½CV²=Q²/(2C). The half factor comes from the average voltage during charging.

Choose the form matching known Q, V or C and keep units in farads, volts and coulombs.

A 100 μF capacitor at 20 V stores 0.020 J.

Using QV without the half factor doubles the energy for a capacitor charged from zero.