In April 1820, Hans Christian Ørsted noticed that the needle of a nearby compass deflected briefly from magnetic north each time the electric current of the battery he was using for an unrelated experiment was turned on or off. Upon further investigation, he showed that an electric current flowing through a wire produces a magnetic field. In 1831 Michael Faraday and Joseph Henry separately expanded on Ørsted's discovery by showing that a changing magnetic field produces an electric current. Heinrich Lenz found in 1833 that an induced current has the opposite direction from the electromagnetic force that produced it. This paper describes an experiment that can help students to develop an understanding of Faraday's law and Lenz's law by studying the emf generated as a magnet drops through a set of coils having increasing numbers of turns.

Topics
General procedures and instrumentation, Faraday's law, Electromagnetic induction, Electrodynamics, Magnetic materials, Batteries, Education, Physicists, Journal
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Sources of suitable hardware and software include Vernier
(www.vernier.com), PASCO (www.pasco.com), and Pico Technology (www.picotech.com).
© 2013 American Association of Physics Teachers.
2013
American Association of Physics Teachers
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