Energy stored in an inductor

An inductor, like a capacitor, stores energy; this time in the form of a magnetic field. Bringing the current from $0$ to $i$ costs work, because the inductor opposes the increase (self-induced voltage): that work remains stored.

Energy in an inductor

$\ev{E_L = \frac{1}{2}\,L\,i^2}$

The formula is the exact analogue of the energy in a capacitor, $E_C = \tfrac{1}{2}\,C\,V^2$. The dictionary of correspondences is by now familiar: where the capacitor uses capacitance $C$ and voltage $V$, the inductor uses inductance $L$ and current $i$.

This energy is not lost: it is returned when the current decreases back towards zero. It is precisely this reversible exchange between electrical energy (in the capacitor) and magnetic energy (in the inductor) that makes the indefinite oscillations of the LC circuit possible.

Collegamenti

Argomenti: Electromagnetic induction Concetti: Inductance and self-induction · Field energy density

Esercizi collegati: Problem — Energy in the field of a solenoid · Graphs of self-induction · RL transient: time constant