Challenges to Faraday's flux rule

摘要

Faraday's law (or flux rule) is beautiful in its simplicity, but difficulties are often encountered when applying it to specific situations, particularly those where points making contact to extended conductors move over finite time intervals. These difficulties have led some to challenge the generality of the flux rule. The challenges are usually coupled with the claim that the Lorentz force law is general, even though proofs have been given of the equivalence of the two for calculating instantaneous emfs in well-defined filamentary circuits. I review a rule for applying Faraday's law, which says that the circuit at any instant must be fixed in a conducting material and must change continuously. The rule still leaves several choices for choosing the circuit. To explicate the rule, it will be applied to several challenges, including one by Feynman. (C) 2004 American Association of physics Teachers.