A copper ring leaps off an electromagnet when it's turned on. What happens when the ring's resistance is lowered using 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: And this is an AC powered electromagnet. And this is a copper ring.
When I place the copper ring on the electromagnet and turn it on, the magnet's changing magnetic field will induce an electric current in the copper ring. The current in the ring will then create it's own magnetic field and the way the math works out, the two magnetic fields will repel each other.
In short when I turn the magnet on the ring flies off!
Steve: Okay! So, while that's cute and all, the ring isn't really going all that high. That's mainly because of resistance in the ring. Now, copper's a good conductor, but it isn't perfect. It still has some resistance that fights the flow of electricity. Now, we can reduce the resistance if we cool the ring down. And, since Joanna always seems to have a supply of liquid nitrogen with her wherever she goes we're going to cool the ring down with that!
Joanna: You can think of resistance as friction for electricity. It changes electrical energy into heat. Sometimes, this is good. For example, toasters wouldn't get hot if they didn't have any resistance. Most of the time, however, this is just a waste of energy. Cooling the ring lowers its resistance. This is like reducing friction. If the resistance is lowered, less heat will be made and more of the energy can go into making the ring jump into the air.
Now that the ring is cold it jumps a lot higher!
Steve: Thank you!
While we reduced the ring's resistance, we didn't get rid of it. You see the frost on the ring? If I hold the ring on the magnet, electricity runs around the loop. The resistance changes some of the electrical energy into heat and the ring warms up. When the ring gets warmer than freezing, the frost disappears!
Joanna: Thanks for watching! I hope you'll join us again soon for another experiment!
Steve: So, how badly do you think we damaged the ceiling?
Joanna: Umm. Not too badly. I don't think they'll notice!
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