5K10.XX Electromagnetic Induction in a Closed Loop


Induction of a current in a closed loop due to a changing magnetic field


A search coil lights up when placed in certain orientations in and around a degaussing coil. It is brightest when the search coil is in the centre of the degaussing coil and is perpendicular to the direction of the changing field. The bulb is dark (no current produced) when the search coil is parallel to the changing field. 



  • [1] Search coil (a closed wire loop attached in series to a bulb)
  • [1] Degaussing coil

Important Notes

  • The degaussing coil becomes hot over time. Turn off when not in use.
  • The apparatus is small, but the bulb is visible in large lecture halls when the lights are dimmed.


  1. Plug in and turn on the degaussing coil.
  2. Hold the search coil in the centre of the degaussing coil.
  3. Rotate the search coil to demonstrate that the bulb lights up in some orientations, but not in others.
  4. Move the search coil around the degaussing coil.


Additional Resources


  • PIRA 5K10.XX


  • Don't attempt this at home!

Last revised

  • 2020


  • Original construction: the coil of wire is a 100' spool of 20 gauge hook up wire. The two ends of the wire were soldered to a bulb to produce a closed loop with the bulb in series. The degaussing coil was purchased.

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.