AAPT Abstract Archive

Abstract Information

  Session: Introductory Courses II
  Paper Type: Contributed
  Title: Four Derivations of Motional EMF
  Meeting: 2015 Summer Meeting: College Park, Maryland
  Location: N/A
  Time: 2:20PM
  Author: Carl E. Mungan, U.S. Naval Academy
410-293-6680, mungan@usna.edu
  Co-Author(s): None
  Abstract: The introductory-level formula for motional EMF can be obtained a number of different ways. It is instructive to lead students through the different derivations in the following specific sequence, because each method brings out a different important aspect of the situation. The first three ways can be used with majors and non-majors alike. The last approach is optionally for physics majors who have been exposed to the idea that a magnetic field is an electric field viewed in a moving reference frame. (1) Apply Faraday's law to a conducting bar sliding on a U-shaped wire. (2) Use work to calculate the change in electrostatic PE of mobile charges driven along a conducting bar moving in a magnetic field. (3) Consider the balance between the applied and magnetic-braking powers as a conducting bar slides on a U-shaped wire at constant velocity. As a bonus, verify Lenz's law. (4) Compute the emf as the integral of the electric field in the bar's frame which is the transform of the magnetic field in the lab frame.
  Footnotes: None
  Presentation: Mungan2015.pdf

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