In an RC circuit the capacitor stores energy. When we discharge the capacitor the energy generally gets dissipated in a resistor. A similar thing happens in an RL circuit where the inductor stores energy.

For an inductor

U

=

LI2 2

This is similar to the equation for the energy stored in a capacitor:

U

=

C DV2 2

Whenever there is an electric field or a magnetic field the field stores energy. This can be viewed in terms of the energy density, the energy per unit volume.

Energy density in a magnetic field:

uB

=

B2 2 mo

Energy density in an electric field:

uE

=

eo E2 2

Note the similar forms, and that the stored energy is proportional to the square of the magnitude of the field.