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Re: [Phys-l] Magnetic force and work



Perhaps this analysis of the work done in the somewhat related motional emf situation will be helpful:
http://lists.nau.edu/cgi-bin/wa?A2=ind0204&L=phys-l&D=0&H=0&O=T&T=1&P=65136

In the above it is shown that in the motional emf situation, the B field force does zero net work. All of the work is done by the agent maintaining the constant velocity of the moving conductor. In the motor situation, an analogous analysis can be done, showing that the work is done by the agent (typically, an emf) maintaining the constant current.

This is only to shed some (perplexing) light on the problem which you raise. In this context, I have real difficulty specifying the working agent in the case of your released two magnet situation. I only intensify the question - I have no good answer : )

A vague hand-waving stab would say that the energy must come from the electromagnetic fields, which must change as the magnets move together. This explanation would invoke induced ELECTRIC fields to do the work.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@velocity.net

----- Original Message ----- From: "Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>
To: <phys-l@carnot.physics.buffalo.edu>
Sent: Wednesday, March 22, 2006 5:23 PM
Subject: [Phys-l] Magnetic force and work


. . .
If I take the two magnets up into outer space (no other influences) and
align them co-linearly so the South pole of one is near the north pole
of the other and let go, they'll accelerate toward each other. Does
this contradict the idea that magnetic forces do no work.
. . .