PURPOSE: To demonstrate a very simple unipolar motor
DESCRIPTION: A "motor" is formed as shown in the photograph at the left above: a cylindrical magnet (with its field along the axis of the cylinder, is stuck to the head of a nail with a small aluminum flag between the two, as seen in the photograph at the center above. The tip of the nail is then held by the magnetic field onto the positive end of a battery as seen in the picture at the left. A wire soldered to the negative end of the battery is then touched to the magnet, creating a current loop. The vxB force causes the nail and magnet to rotate clockwise as seen from above. Note that the actual vxB force on the wire is counterclockwise, but the reaction force on the magnet causes the magnet and nail system to rotate clockwise.
Click your mouse on the photograph at the left above to see an mpeg video of the action.
SUGGESTIONS: See Question of the Week #284 for information on using this demonstration to enhance class involvement.
Here is a photograph of a similar unipolar motor used as a hallway demonstration, provided by Doug Johnson of California State Polytechnic University, Pomona, CA.
Click here to see a really slick homopolar motor created by Dr. Julio Palacios, shown on his web site, Fundacion Julio Palacios, http://www.fjp.org.ar/index.htm.
REFERENCES: (PIRA 5K40.10)
EQUIPMENT: Unipolar motor.
SETUP TIME: None.
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