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Why is the permament magnet not completely attracted to the superconducting magnet?

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Bararontok
#1
Oct14-11, 07:28 AM
P: 298
It is possible for a permanent magnet to be attracted to a cooled superconductor magnet as shown in many experiments, but why does it not attract the permanent magnet to the point that their surfaces come in direct physical contact similar to the attraction that causes two permanent magnets join together when their opposing poles are placed in sufficient proximity? There are many videos showing the permanent magnet levitating above the superconducting magnet and requiring a certain amount of force to be pulled away, but when the permanent magnet is pressed against the superconducting magnet, it bounces back to a specified height like a spring. Why is this happening?

Another interesting question is how the magnetic field of the superconductor remains stable even when the external magnetic field of the permanent magnet exerts a torque that breaks the alignment of the anti-parallel electron pairs that lose their dipole alignment easily because anti-parallel arrangements have difficulty generating the persistent mass magnetic field in the first place.
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xts
#2
Oct14-11, 08:15 AM
P: 882
Quote Quote by Bararontok View Post
There are many videos showing the permanent magnet levitating above the superconducting magnet and requiring a certain amount of force to be pulled away, but when the permanent magnet is pressed against the superconducting magnet, it bounces back to a specified height like a spring. Why is this happening?
Those videos shows permanent magnet levitating over a surface of superconductor, not over superconducting magnet. Superconductors are ideal diamagnetics, so they are repelled from magnetic field (and - 3rd law of dynamics - equally repell magnets)

Superconducting magnets are something quite different - they are ordinary electromagnets with yokes makes of some ferromagnetic substance (iron, ferrite...), but their coils are made not of copper wire, but rather of superconducting wire - which may conduct extremely high current without any resistance, so without dissipating any power, which - in case of copper coil - would melt it quickly.
Bararontok
#3
Oct14-11, 09:14 AM
P: 298
So that means that the permanent magnet is not being attracted to the superconductor but is instead being repelled and the superconducting magnets are not permanent magnets but electromagnets with the difference being that the superconducting electromagnet has no resistance.

But if this is the case then why did one experiment video show a superconductor following the permanent magnet when it was lifted away and yet it was also repelled when the permanent magnet was pushed too close. Additionally, this superconductor was only cooled by liquid nitrogen and it had no power supply which means that it is a permanent and not electromagnet.

But then again, the superconductor needs no persistent mass magnetic field to be attracted to a permanent magnet because permanent magnets can attract metals even when those metals are demagnetized and exert no external magnetic field. This is due to the many excess electrons possessed by metals being attracted to the external magnetic field. The only question is why the permanent magnet can be attracted to the superconductor but not to the point that it sticks to the surface of the superconductor?


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