Inductor Delaying A Lamp


To demonstrate the timing of current in a switched inductor circuit by asking students a question.


7.5 volt battery, knife switch, two light bulbs, large (approximately 0.92 henry) inductor.


Setup Time

5 min.




    An inductor and light bulb are connected across a battery with a switch. In parallel with this inductor and◙light bulb is a second identical light bulb. Q: Predict what the light bulbs will do when the switch is closed. A: The separate light bulb will light immediately, but the light bulb in series with the inductor will be delayed in lighting until the current reaches a high enough level. The delay time is related to the L/R time constant of that leg of the circuit.◙