Energy in an Inductor

When a electric current is flowing in an inductor, there is energy stored in the magnetic field. Considering a pure inductor L, the instantaneous power which must be supplied to initiate the current in the inductor is

so the energy input to build to a final current i is given by the integral

Using the example of a solenoid, an expression for the energy density can be obtained.

Energy in Magnetic Field

Solenoid Field Solenoid Inductance	From analysis of the energy stored in an inductor, the energy density (energy/volume) is so the energy density stored in the magnetic field is