ittle Gems Christopher Chiaverina, Column Editor 4111 Connecticut Trail, Crystal Lake, IL 60012 firstname.lastname@example.org Levitated Homopolar Motor H. K. Wong, Physics Department, The Chinese University of Hong Kong, Hong Kong, P.R. China; email@example.com number of homopolar motors have been described in this journal and elsewhere.1-9 The new one described here has some very interesting features. Its construction is shown schematically in Fig. 1. Neodymium magnets (disks 1.5 cm in diameter and 0.5 cm thick) are placed at the ends of a AA battery. An aluminum foil tube (~1.6 cm diameter) is made by wrapping a piece of foil (~6 cm x 15 cm) around a whiteboard marker. The tube is slightly longer than the magnet-battery array. When the highly conducting tube is positioned around the array as shown, it momentarily short circuits the battery. The magnetic force on the flowing current results in a torque that causes the tube to rotate. Faint sparks can be observed between the tube and the magnets; the instantaneous current can be more than 8 A. Because of this, we prefer using a rechargeable NiMH battery due to its good performance for high drain. Occasionally the magnets can get too hot to be touched. If properly aligned, the rotating tube is levitated due to the motional N S Al foil tube S N Fig. 1. Levitated homopolar motor. The aluminum foil tube rotates about the magnet-battery array. emf (an effect due to the motion of the conducting foil through the magnetic field).10 A video clip is available online.11
The Physics Teacher – American Association of Physics Teachers
Published: Feb 1, 2009
Keywords: physics education; educational aids; electromagnetism; homopolar motors; magnets; foils; electric current
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