Physics Dept. Demonstration Manual

DEM53 - Stored Energy in an Inductor


To show that an inductor is capable of storing energy.

  • inductor (1.5 H)
  • lamp (6 V, no. 40)
  • resistor (2.7 ohms, 2 Watts)
  • knife switch, SPST
  • battery (6 V)


Initially the switch is open. At the moment the switch is closed, the lamp will be fairly bright for an instant and then remain dim at steady state. (An inductor exhibits the electrical equivalent of inertia, as the initial response to a change in current is delayed, or "lags." During that moment, most of the current flows through the lamp. When the delay or lag is complete, current will flow through the inductor, which is connected in parallel with the lamp. At this time, the bulb is then dim, since most of the current is flowing through the parallel inductor.)

At the instant the switch is opened, the stored energy in the inductor is dumped into the parallel bulb, resulting in a brilliant flash. (The series resistor serves only to limit inrushing current during turn-on.)