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Re: [Phys-l] drop a metal cylinder through a solenoid




On 2012, Mar 21, , at 14:17, Carl Mungan wrote:

If we drop a permanent magnet through an aluminum pipe, the magnet
falls slowly due to eddy current loops induced above and below the
falling magnet.


cut


reminds me of:




So, What WOULD Happen If a Magnet Were Dropped Down a Superconducting Tube?
..... or.....The Meissner Effect Revisited
Ron Brown
Department of Physics
Cal Poly San Luis Obispo

It has been nearly fifteen years since this question first was posed to a small group of physicists and physics teachers - including, John Rigden, David Goodstein, and Richard Feynman, and a number of others - immediately following a meeting of the Southern California AAPT (November, 1987). The animated discussion of the many speculations that followed was sheer joy. Then a surprising answer was offered by Caltech's Goodstein - which evoked an immediate and gleeful "Of course!" from Feynman (and I might add, from the rest of us as well!). It was like being on hallowed ground, as John Rigden was later to write. The question is, what did Goodstein say that the rest of us agreed with so quickly? And why do we think his answer was right? This discussion will include how magnets and superconductors interact, Faraday's law, the Meissner effect, and London's equation, magnetic forces, induced currents and persistent currents - and which of those principles and ideas are important to answering this question. And the answer will be clear.

bc

p.s. AAPT Joint Meeting [Norcal and Socal sections 2002]
Friday, April 26 – Cal Poly San Luis Obispo