Magnets in Pipes!

Magnets in Pipes!


Frostbite Theater presents… Cold Cuts! No baloney! Just science! Hi! I’m Joanna! And I’m Steve! 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. Now, of course, the real question is, ‘What if you cool the pipe in liquid nitrogen?’ Luckily, we just happen to have some! Cooling the pipe lowers its resistance. 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. 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. 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! Thanks for watching! I hope you’ll join us again soon for another experiment! So, you know what we need to do? We need to cover that refrigerator with artwork. Yes! Stickman Steve! Just finger paint all over it. I’m sure they would love that. They would love that if we did that! Yeah.

30 Comments

  1. Is it cooled below the temps of liquid helium? If so how do you get colder than that, isnt liquid helium the coldest liquid?

  2. Hi! Does the magnet fall through the copper pipe at a constant rate or is it accelerating some due to gravity? My guess is constant rate but I'd sure like to find out for sure. Thanks!

  3. Does the helium leak over time? If so, what do you do to mitigate losses (especially in light of the helium supply problem)?

  4. Hey I actually live in Hampton and have friends who aspire to work at Jefferson Lab one day, someone in the comments asked the question what would happen if the magnet was cooled. What would happen in this circumstance? Would it just have the same effect?

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