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Re: jumping ring demo



Paul Johnson's formulation of Lenz's law: "The induced
current is always in a direction opposite to what you
calculate" was very nicely put.

Lenz's law appears to me to be used more as a prop to faulty
reasoning, a pair of magic words, than as a useful adjunct
to Faraday's law.

I don't like the word law (much less Law) being used in
relation to it. In their excellent text Chabay and Sherwood
refer to "Lenz's rule" and that's what it is a rule of thumb
to aid in tracking down what direction the - sign in
Faraday's law is telling us is the direction of the
non-Coulomb electric field. As Chabay and Sherwood state it
we imagine that we place a wire around the changing flux, so
that the non-Coulomb electric field drives current in the
(imaginary) wire in a direction to make a magnetic field
that attempts to keep the flux constant. So well put.

Brian McInnes