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[Phys-L] Lenz's law and conservation of energy

Hi Phys-L, Antti, John D,
-Can you tell me how Lenz' Law works with maglev trains.
-I cannot for the life of me see how a moving vehicle supported in a
magnetic field would not create eddy currents which would dissipate a
substantial portion of the mechanical energy of the train.
Bill Norwood
U of MD at College Park

On Mon, Mar 31, 2014 at 12:23 PM, Savinainen Antti <> wrote:


thanks for the comments. I agree that the question is quite bad. I think
that the intention of the examinors was the following:

When there is a changing magnetic flux through a conducting loop, an emf
is induced and in this case a current as well. The current has an
associated magnetic field which must oppose the change in the magnetic
flux. If it didn't, it would contribute to the change in magnetic flux and
subsequently create a greater induced current. This would violate the law
of conservation of energy.

John D. is right in writing "One of the standard tricks for gaming the
test uses the "principle" stated by Sherlock Holmes: when you have
eliminated the impossible, whatever
remains, however improbable, must be the truth." I hope that questions in
fortcoming exams will be of higher standard.



Viesti on tarkastettu roskapostinsuodatus- ja virustorjuntaohjelmistolla.

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