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Frostbite Theater

Magnets in Pipes!

Take a strong magnet and drop it down a copper pipe. You'll notice that the magnet falls slower due to magnetic induction. But, what happens if you cool the copper pipe with liquid nitrogen?

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: Have you ever dropped a strong magnet down a copper pipe? If you do, you'll notice that the magnet falls slower than it normally would. This is because the falling magnet induces a current in the walls of the pipe. This current creates its own magnetic field which opposes the motion of the magnet.

Steve: Now, of course, the real question is, "What if you cool the pipe in liquid nitrogen?"

Joanna: Luckily, we just happen to have some!

Steve: All else being equal, if the resistance is lower, then the induced current is higher. A higher current creates a stronger magnetic field which can more effectively oppose the motion of the magnet. In short, the magnet falls slower because copper is a better conductor when it's cold.

Joanna: Some materials lose all of their electrical resistance when they get cold enough. We make use of this property in our accelerator. Our acceleration cavities are made of the element niobium, which becomes superconductive near absolute zero. Because our cavities are superconductive, our accelerator requires less energy to run.

Steve: And, since our cavities need to be kept near absolute zero, our accelerator is lined with thermos bottles filled with liquid helium supplied from the world's largest helium refrigerator!

Joanna: Thanks for watching! I hope you'll join us again soon for another experiment!

Steve: So, you know what we need to do? We need to cover that refrigerator with artwork.

Joanna: Yes! Stickman Steve!

Steve: Just finger paint all over it.

Joanna: I'm sure they would love that.

Steve: They would love that if we did that!

Joanna: Yeah.

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