Magnet Levitates and then Melts Metal

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Cool levitation and heating effects can be done at home — if you happen to have a little specialized electrical equipment and a few tools.

This video shows a piece of metal floating in a coil and then melting. How does this happen? It isn’t magic, just physics.

First the levitation. If you run an alternating current (like the one from the outlets in your house) through coils you generate a magnetic field that changes with time. House current would make it change 60 times per second. (That’s the “60 Hz” you see printed on the power adaptors and appliances when it says what kind of power source you can hook them up to). So the field in that case will oscillate at 60 hertz.

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Put something in a magnetic field — like a chunk of aluminum — and the atoms in the object will generate small currents, called eddy currents that generate small magnetic fields of their own. If the material is diamagnetic, which basically means it doesn’t stick to magnets, then the tiny magnetic fields will be opposite to the one in the coil, and generate a force that repels.

This is largely the same principle used in magnetically levitated trains, which float above their tracks to reach high speeds.

In addition to using a piece of aluminum, the experimenter also used a power inverter to alternate the current at 204,000 times per second, a much higher frequency than what you get from an outlet. It’s also not clear how much current and voltage is being used.

Next up is the heat. The metal melts because of a principle called induction heating — the same principle used in induction stoves.

The heat comes from the magnetic field that levitates the piece of metal. Remember the eddy currents that are generated in the aluminum? Those currents encounter resistance, and in doing so heat the metal up. The more resistance, the more heat.

The piece of metal here is also pretty small — only 2.6 grams, or about the weight of a couple of medium-sized paper clips. So it doesn’t take a lot of energy to melt it.

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None of the equipment to repeat the experiment is that exotic; for instance, a 1,600 Watt power inverter, like that used in the video, can be had for under $100, and another $100 will get you the “deep cycle” batteries.

via Geek

Credit: YouTube (screen grab)