Physics at the University of Virginia
Academics People Research Announcements Facilities Adminstration Home Updates

Return to Demo Lab Homepage

Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

Choose a Topic or Enter a keyword to search:
I cannot find what I want!

You have selected the following Demos:
  • None Selected

Choose a subtopic:
(Clicking a green button will add that demo to your list)
 Electric Fields And Potential
 Current and Resistance
 Electromotive Force And Current
 DC Circuits
 Magnetic Materials
 1x 2x 4x Coils and Bar Magnet
  video  - Hanging Ring and Magnet
 Flash Bulb Coil
  video  - LED Coil
  video  - Eddy Current Pendulum
  video  - Lenz's Law and Eddy Currents
  video  - Eddy Current Tube
  video  - Jumping Ring
 Eddy Current Levitation
 Eddy Current Levitation 2
 Eddy Currents 2
  video  - Transformers
 Electric Motor
 Hand Crank Generator
 Bicycle generator
 Complex Circuits
 Semiconductors And Tubes
 Transmission Lines and Antennas

 video  - Hanging Ring and Magnet


To demonstrate Lenz's Law.


centered image
centered image
  DEMO VIDEO DOWNLOAD / no audio / 1920x1080 / 24.19Mb/s / 283MB size  

  DEMO VIDEO DOWNLOAD / no audio / 854x480 / 5.69Mb/s / 64MB size  

There are two rings:

  • SLOTTED - one ring has a slot machined out of it so that its an effective "open circuit" and no Eddy currents can flow
  • CONTINUOUS - quickly move the magnet in and/or out of the ring, without touching it observing the movement of the ring as compared to the direction of the magnet motion


    The direction of the induced emf and induced current is determined from Lenz’s Law which states that the polarity of the induced emf is such that it will produce a current that will create a magnetic flux to oppose the change in the magnetic flux through the loop.
    If one uses one of the stronger "tablet" magnets attached to a metal rod the movement can be made more obvious. Moreover, with the tablet magnet the direction of the magnetic field can be changed to demonstrate no motion when the field is the ring's plane.