Electromagnetic energy

Electric and magnetic fields store energy. The total energy stored in a volume is the integral of the energy density over the volume.

U = \iiint udV.

Energy stored in an electric field

u_E = \frac{\epsilon_0 E}{2}.

The total energy stored in the electric field of a capacitor is $U = \frac{Q^2}{2C}$ .

u_B = \frac{B}{2\mu_0} .

The total energy stored in the magnetic field of an inductor is $U = \frac12 LI^2$ .