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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.

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 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

Electric Motor


To demonstrate the principles involved in the operation of an electric motor.


In the first image, an example of a "simplest motor" is our Homopolar Motor: consists of just a D-cell battery, ferromagnetic drywall screw, cylindrical neodymium magnet and copper wire. Make sure the copper wire is well sanded and clean at the magnet contact and the D-cell is not low/dead (this motor drains battery rather quickly).

In the second image, the motors are more complicated. The smaller homemade motor with 9V battery, neodymium magnet and copper wire loop has the one side of the rotor wire insulation completely removed, whereas the other side only has 1/2 the insulation removed along its straight length. This configuration turns off the current for half the cycle, letting the angular momentum of the spinning motor carry it through rotation. The larger motor with horseshoe magnet has a commutator on one end (right) to allow operation with DC input (large 6V battery) and constant brush contacts on the other end (left) to allow operation with AC input. One can use this motor as a generator as well, to show DC or AC output.


For the motor with the horseshoe magnet and commutator, align the contacts such that the brushes do not overlap both contacts, ie. the rotator electromagnet should be in the horizontal orientation before applying DC.


  • 6 V Car Battery
  • Connecting Wires
  • Small Electric Motor