5K20.25 Eddy Current Tubes


Faraday's law, Lenz' law, magnetic fields from currents


A magnet falling down a copper tube is slowed by magnetic fields from eddy currents induced in the tube. A magnet falling down a glass tube is unaffected.



  • [2] Lab stand
  • [1] Glass tube
  • [1] Copper tube
  • [2] 3-finger clamp
  • [4] 90-degree clamp
  • [2] Bell
  • [1] Aluminum slug
  • [1] Magnet
  • [1] Plastic container

Classroom Assembly

  1. Set up lab stands, each with a 3-finger clamp holding a tube and a bell mounted just below the tube.
  2. Put the plastic container under the bells to catch the magnet and slug when they fall.


  1. Using either the document camera or overhead projector, show the class that the aluminum slug and magnet are the same diameter.
  2. Put the aluminum slug through both tubes, showing there are no obstructions inside. The bells will ring when the slug hits them.
  3. Put the magnet through the glass tube, showing how it falls as the aluminum slug did.
  4. Put the magnet through the copper tube. In about 8 seconds, it will make a very light "ding" sound on the bell.


Additional Resources


  • PIRA 5K20.25


  • Don't attempt this at home!

Last revised

  • 2017


  • Use a non-ferromagnetic 3-finger clamp to hold the copper tube. Otherwise, there is a small (~10%) chance of the magnet stopping next to the clamp.

Related AV

Related demos

  • Electromagnet
  • Jumping rings
  • Superconducting train
  • AC induction
  • Solenoid induction with a battery
  • Permanent magnet induction
  • Eddy current ramps


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.