Energy Stored in an Inductor:
Assume current through the coil of inductance L henry increases by di amperes in dt seconds then
Induced emf = L( di / dt) Volts
Energy absorbed by magnetic field during time dt second is
iL . (di / dt ). dt = Li . di joules
Therefore, total energy absorbed while current increases from O to I amperes is
W =( ½) LI 2