Flux Trapping Effect: Magnetic Levitation & Suspension Explained

[cartik]

Magnetic suspension and levitation is the caused by the flux trapping effect in superconductors.How does this flux get "trapped"?

Another quick question-
We link a magnet to a superconductor by bringing it very close to one ,until both of them start attracting and repelling. My question is, if the magnetic field strength of this magnet is greater than the critical field of the superconductor,the superconductor will lose its properties and become normal, instead of demonstrating magnetic levitation and suspension ,right ?

 

[FeynmanIsCool]

This phenomena is called the Meissner Effect. Wikipedia offers a great explanation of the subject. If you are looking for a mathematical explanation, you should look up the "London Equations" I believe the explain the expulsion of flux mathematically.

http://en.wikipedia.org/wiki/Meissner_effect
http://en.wikipedia.org/wiki/London_equations

 

[f95toli]

Magnetic suspension and levitation is the caused by the flux trapping effect in superconductors.How does this flux get "trapped"?

No, magnetic suspension/leviation is caused by the Meissner effect. Flux trapping is what makes magnets levitating over type II superconductors stable, if it wasn't for the trapped flux the magnet would fall off or slide to the side (it is possible to do this without trapped flux, even in type I systems, but it is very tricky to find a stable configuration).

The flux lines are trapped around impurties, gain boundaries etc. The math is quite complicated, but can be found in standard textbooks (see e.g. Tinkham)

Another quick question-
We link a magnet to a superconductor by bringing it very close to one ,until both of them start attracting and repelling. My question is, if the magnetic field strength of this magnet is greater than the critical field of the superconductor,the superconductor will lose its properties and become normal, instead of demonstrating magnetic levitation and suspension ,right ?

Yes, if the field is larger than the critical field the superconductor will just turn into a normal metal (or whatever the normal state is for that material).