5K10.82 - Homopolar Motor as a Generator

Code Number:
Demo Title:
Homopolar Motor as a Generator
Motors & Generators
Area of Study:
Electricity & Magnetism
Homopolar Motor Unit and Roller with internal magnets, Large Gray Lecture Galvanometer or the Large Older (Ancient) Black Lecture Galvanometer.

See: 5H40.53 - Homopolar Motor and 5H40.38 - Lorentz Force With a Twist demonstrations. 

Connect the Unit to the gray or ancient black lecture galvanometers.  ( These two have the best sensitivity for this demonstration ).  Slide the copper pipe containing the two cylindrical magnets on the rails and notice that there is little to no deflection of the galvanometer pointer.  Now roll the copper pipe on the rails and note the observed deflection of the galvanometer pointer.  The TPT, Vol. 36, #8, Nov. 1998, p. 474 article explains this behavior very well.

  • Keith Zengel, "The Handheld and Hand-Powered Homopolar Generator", TPT, Vol. 56, #1, Jan. 2018, p. 61.
  • H. K. Wong, "Motional Mechanisms of Homopolar Motors & Rollers", TPT, Vol. 47, #7, Oct. 2009, p. 463.
  • Norihiro Sugimoto and Hideo Kawada, "The Homopolar Motor and Its Evolution", TPT, Vol. 44, #5, May 2006, p. 313.
  • Robert Beck Clark, "The Simplest Generator from the Simplest Motor?", TPT, Vol. 44, #2, Feb. 2006, p. 121.
  • Bill Layton, Martin Simon, "A Different Twist on the Lorentz Force and Faraday's Law", TPT, Vol. 36, # 8, Nov. 1998, p. 474.
  • Jorge Guala-Valverde, Pedro Mazzoni, and Ricardo Achilles, "The Homopolar Motor: A True Relativistic Engine", AJP, Vol. 70, #10, Oct. 2002, p. 1052.
  • Robert D. Eagleton and Martin N. Kaplan, "The Radial Magnetic Field Homopolar Motor", AJP, Vol. 56, #9, Sept. 1988, p. 858.
  • Robert D. Eagleton, "Two Laboratory Experiments Involving the Homopolar Generator", AJP, Vol. 55, #7, July 1987, p. 621.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.