Superconductivity + liquid nitrogen + magnet

[Zidane]

Hey guys  !!! this question is not part of the study design (i think....?? lol )

here it goes ...

so there's a prac where liquid nitrogen is added on  Cu2O and then a magnet is placed on top of the Cu2O , which starts floating!!!   i know that by adding liquid nitrogen to the ceramic you make it a superconductor  (as it loses all of its electrical resistance) which enables it to induce powerful magnetic fields, but i don't get why the magnet floats. could someone please explain?
Thanks guys 

[mark_alec]

What do you know about Lenz's law?

[Zidane]

What do you know about Lenz's law?

E = -n B.A / t

an emf is induced only if (B.A) changes.
the induced emf causes a current to flow, which will set up its own magnetic field. the direction of this magnetic field will (oppose the change) in the external magnetic field that induced the emf in the first place.

[mark_alec]

Consider what happens when the magnet is pushed towards the superconductor. How does the magnetic field produced by the magnet change? What current and field would be induced in the superconductor as a result of this? And what do you know about magnets with the same pole?

[Zidane]

Consider what happens when the magnet is pushed towards the superconductor. How does the magnetic field produced by the magnet change? What current and field would be induced in the superconductor as a result of this? And what do you know about magnets with the same pole?

im having a guess here would the magnetic field not enter the superconductor. so it would be repelled back to the magnet?? and we know that like charges (poles) repel, hence that means that opposing poles will cancel each other out causing it to float in the air?? 

[mark_alec]

It isn't that the magnetic fields bounce back - if you draw the field lines you will see that this is impossible as magnetic field lines cannot cross. Instead surface currents are induced in the superconductor, which produces a magnetic field that then produces a force on the magnet.

Although it isn't in the course, you could look up the Meissner effect and London equations for a more quantative explanation.

[Zidane]

It isn't that the magnetic fields bounce back - if you draw the field lines you will see that this is impossible as magnetic field lines cannot cross. Instead surface currents are induced in the superconductor, which produces a magnetic field that then produces a force on the magnet.

Although it isn't in the course, you could look up the Meissner effect and London equations for a more quantative explanation.

ahh that kind of makes sense. ill definitely check The meissner effect

Thanks for your help!!