Name: 莫比斯帶材上的懸浮超導體 (Levitating Superconductor on a Mobius strip)
Uploaded: 2021-01-14T08:33:00.000Z
Duration: 7 min 30 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

I wanted to show you one of my favourite props from last

year's Christmas Lectures, which is a Mobius strip steel

track, covered in maybe 2,000 or 3,000 of these super strong

So what I want to show you is how this track is going to

This is a high temperature superconductor, made of

And a superconductor is something that, when you cool

it down, in this case with liquid nitrogen, it loses all

So this leads to some interesting behaviours, which

And to do that I'm going to need to hang this thing from

So we have one suspended, super strong, neodymium

What we need now is some liquid nitrogen.

So we're down in one of the labs at the RI.

And this is where the liquid nitrogen is stored.

The superconductor is now cooling down, which will take

It needs to be cooled down in situ, because, one, what I'm

trying to get to is to have a superconductor kind of locked

So I need to cool it down in situ above the track.

I'm cooling it down past it's critical temperature, the

temperature at which it will become a superconductor, and

its electrical resistance will completely disappear, which is

And the burger tray is there to maintain the spacing

between the superconductor and the track.

So that is the position that we want it to take up.

This is the best way I've found of doing this.

If you ever hold it so quickly enough you can see that it's

Actually, you might be able to see a gap underneath it there,

So unfortunately, it warms up quite quickly.

Obviously, the effect only works as long as it is at its

So what's actually going on there, a good way to start to

understand that is to think about how magnets interact

with ordinary conductors, like this copper tube.

So if I just drop this nut through, it falls all the way

If I drop a strong magnet through instead, it takes

So the reason that's happening is as the magnet moves through

Those electric currents, themselves, have their own

And that magnetic field will always arrange itself so as to

This is the fundamental principle of electromagnetism,

And the conductors are moving conductors near magnets,

Now, because this is not a superconductor, because it has

electrical resistance, the currents that are created as

the magnet falls through will always tend to die away.

So if the magnet were, for instance, to be stopped by the

electric currents, those currents would immediately die

away, and the magnet would start falling again.

So what actually happens is it just falls

If, however, this were a superconductor those currents

As soon as you induce them by introducing the magnets into

the tube, those currents would remain and would keep going

and would keep going even after the magnet has stopped.

So if this were a superconductor, the magnets

They would be effectively levitating in the pipe

And to do that, we saw, when I was demonstrating the

superconductor on the track down here, that the effect

It warmed above its critical temperature and stopped

The solution we've decided on for the Christmas Lectures

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莫比斯帶材上的懸浮超導體 (Levitating Superconductor on a Mobius strip)

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