5K20.25-Magnets and Eddy Tubes


Video: Watch this demo | Demo #2

Instructor’s video

MIT Demo Video

Description: This demonstration shows properties of Lenz’s Law via a magnet falling through a conductive tube


  • metal tube
  • cylindrical magnet
  • non-magnetic cylinder

Demonstration Procedure:

  1. Holding the metal tube with the bottom of the tube near the floor, drop the non-magnetic cylinder through the tube (note how long it takes to fall)
  2. Drop the cylindrical magnet through the tube, again note how much longer it takes to fall

Concepts: The moving magnet generates eddy currents in the surrounding conductive tube. These eddy currents interact with the magnet, resulting in a force that slows the magnet’s falling speed. The non magnet will fall down the tube quickly due to there being no present magnetic fields or forces.