Northwestern Physics Demos                                 Go back to Magnetism   
DCS#  5J10.20NWU#  E-09Location: Lab Bench
title: Energy Stored in an Inductor
aka:  Back EMF

    A 1.0 henry inductor (heavy!) is attached to a double throw knife switch so that a current of 3 amperes can be produced in either the inductor or a resistor (adjusted for 3 A).
   The current rise time is noted for the reisitor and compared to that of the inductor.
   When the current is interupted in the inductor, a large spark appears on the knife switch, but not so with the resistor.
   A neon lamp can be attached across the inductor terminals to also flash with the back emf.

    Can this spark damage a switch?
    Do motors have inductance?
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