5L10.10-Variable Inductance

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Video: Watch this demo

Instructor’s video

Description: This demonstration shows that a variable inductor connected in series with a light bulb will dim as the inductance is increased.


  • VariAC
  • Large variable iron core inductor
  • 150W light bulb
  • SPST switch
  • C clamp
  • VariAC to banana plug cable
  • Banana cables

Setup Procedure:

  1. Connect the equipment as shown in the diagram.
  2. Clamp the switch down to the table using a C clamp.
  3. Set the VariAC to 60VAC
  4. Test that the light bulb starts off bright, and then dims when you put the iron core into the inductor.

Demonstration Procedure:

  1. Turn on the VariAC.
  2. With the iron core inductor out, close the switch and note how bright the light is.
  3. Then insert the iron core into the inductor and note that the light bulb dims. This is because the higher inductance impedes the flow of the AC current.

Note: Careful when inserting the iron core into the inductor when the power is on.
If the magnetic field is strong, the iron core may get pulled out of your hand.