Magnetic fields and superconductors

[Forestman]

1. I have read that external magnetic fields cannot penetrate a superconductor. Why is this?

2. Does the magnetic field produced by the superconducting current extend outside of the superconductor? And if so, what happens when the magnetic field starts to collapse, can it renter the superconductor?

 

[malawi_glenn]

1. The Meissner effect

2. Yes it does, if i remember correctly, but I let someone else answer with more precision ;)

 

[Forestman]

Thanks malawi glenn

 

[miketem]

Just add a bit Mr malawi gleen explanation,,,

1. Superconductor is a perfect dia-magnetic. When you apply an external magnetic field it will create a magnetic field that oppose the external one so it's repel the magnet. The magnetic field still remain since the free electron continues moving even there's a collision, the energy lost extremely small.

2. Yes, until you give a heat to the superconductor or bring to the room temperature. cause superconductor effect only operate at very low temperature.