A number of interesting demonstrations of induced electric currents and of Lenz's law have been described in this journal.1–5 In this paper, a simple version of an experiment that was described6 by Léon Foucault in 1855 is presented. Foucault placed a rotating copper disk between the poles of an electromagnet. When the electromagnet was off, the disk rotated almost without friction, but when the electromagnet was turned on, the disk stopped almost immediately. Nice discussions of this sort of magnetic braking may be found in a number of textbooks.7 Here I describe how to do the demonstration quite simply using recycled materials.
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Eugene Hecht, Physics (Calculus) (Brooks/Cole, 1996), pp. 846–847.
8.
See PASCO Catalog, Lenz's Law Demonstrator, # MG-8600, http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51814&Detail=1. Also Arbor Scientific Catalog, Lenz's Law Apparatus, # P8-8400, http://www.arborsci.com/Products_Pages/Magnetism/Magnetism4.htm, and CENCO Catalog, Lenz's Law Apparatus, # CP32691-00, http://www.sargentwelch.com/product.asp_Q_pn_E_CP32691%2D00%5FEA_A_Lenz%27s+Law+Apparatus%2C+CENCO_E_.
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© 2006 American Association of Physics Teachers.
2006
American Association of Physics Teachers
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