Some questions on properties of superconductors

[Crusoe]

Hi all,

I was wondering if someone can explain to me whether:
1) Superconductors are attracted to originally unmagnetised ferromagnetic or paramagnetic materials?

AIUI superconductors are perfect diamagnets due to the Meisnner Effect, and magnetic attraction is due to the creation of induced magnetic moments in the above materials, which in turn produce magnetic fields which mutually attract.

2) Following on from 1, what happens if you bring a superconductor in proximity to iron filings?

3) Whether very large eddy currents can be induced in a superconductor by a changing EM field, e.g. brushing a permanent magnet past a superconductor or the superconductor being in close proximity to an AC power cable.

4) Is there a way of determining the current density and direction of eddy currents induced in a superconductor?

5) If a superconducting disk had induced eddy currents in it, and a part of it was changed to a non-superconducting state (e.g. heated up), what will happen?

Thanks.

Doc Crusoe

 

[Relay]

Search for "superconductor" on "www.youtube.com". Those videos will explain most of your questions.

 

[sir-pinski]

Hi Doc Crusoe,

1) Superconductors are attracted to originally unmagnetised ferromagnetic or paramagnetic materials due to the Meissner Effect, which is the expulsion of magnetic fields from the interior of a superconductor. This creates a repulsive force between the superconductor and the magnetic material, causing the superconductor to be attracted to it.

2) If you bring a superconductor in proximity to iron filings, the filings will be attracted to the superconductor due to the Meissner Effect. However, if the superconductor is cooled below its critical temperature, the magnetic field will be expelled and the filings will no longer be attracted to it.

3) Very large eddy currents can be induced in a superconductor by a changing EM field. This is because superconductors have zero resistance, so they can conduct electricity without any energy loss. This allows for a large amount of current to be induced by a changing magnetic field.

4) The current density and direction of eddy currents induced in a superconductor can be determined by measuring the magnetic field around the superconductor. The direction of the magnetic field will be opposite to the direction of the induced current, and the strength of the field can be used to calculate the current density.

5) If a superconducting disk had induced eddy currents in it and a part of it was changed to a non-superconducting state, the eddy currents would decrease in strength as the resistance of the disk increases. This is because the non-superconducting part of the disk would act as a barrier to the flow of current, causing a decrease in the induced eddy currents.

I hope this helps! Let me know if you have any further questions.