Superconductors and Magnets

Due to the Meissner effect, a superconductor will levitate above a magnet. But what if you induce persistent current in the superconductor to make it a magnet?


How is that superconductor staying at below critical temperature in ambient room temperature air?
Also he seems to be touching it with his bare fingers. If you touch dry ice it hurts. How can he touch it?
I am surprised those superconductors warm up so slowly.


It looks to me like he just took the superconductors out of a liquid nitrogen bath before doing the demonstrations. You can see the condensation from the atmosphere indicating they’re cold. High T_c superconductors are basically ceramics, so they don’t conduct heat well. Heat will flow from the outside in, and as long as the bulk is below the critical temperature, it probably doesn’t matter if the outside skin is resistive.

If you squeeze dry ice, it freezes your skin, but if you hold it very lightly, there isn’t enough conduction to cause a problem. (There’s also the leidenfrost effect of sublimating CO₂, but that doesn’t happen with the superconductor.) It looked to me like he was holding the superconductors lightly.

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10-4 :slight_smile:

Off topic but every time I see the word superconductor I think of this project that was cooking in the late 80s in the Dallas area called the superconductor/supercollider. If memory serves it was about some energy producing scheme that never got going.