Question

An air-filled 20-μf capacitor has a charge of 60 μc on its plates. how much energy is stored in this capacitor?

Answer 1

Thew energy stored in a capacitor of capacitance $C$ and voltage between the plates $V$ is

$E=\frac{1}{2} CV^2=\frac{1}{2C} Q^2$.

Substituting numerical value

$E=\frac{1}{2*20*10^{-6}} (60*10^{-6})^2\\ E=90\; \mu J$