Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: ad.hiatt on 14/07/2014 10:38:17
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I am looking to make an electromagnet repel something (metal, or another magnet?) with a fair bit of force. Is this possible or do electromagnets only attract? This is actually something that Google is failing to give a good enough answer to...
I suppose another way to ask this question is, what is strongly repelled by an electromagnet?
Thank you kindly for the assistance.
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Electromagnets, like permanent magnets have two poles, N & S.
Like other magnets, like poles repel (N - N, & S - S), and dissimilar poles attract (N - S & S - N).
There is a class of materials known as diamagnetic. These materials are essentially repelled by all magnetic fields (both N & S). Some of them are stronger at very low temperatures near absolute zero. Superconductors are generally diamagnetic.
Water is weakly diamagnetic, and would be repelled by an extremely strong magnetic field.
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What is strongly repelled by an electromagnet?
Another magnet or electromagnet. To the same pole.
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An electromagnet running on AC will repel a conductive metal sheet (The London science museum has such a demonstration setup in the children's section)
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If you want to repel something in a particular direction, attach a permanent magnet to a frame so it can only move in and out, without spinning around. Then an electromagnet can repel the permanent magnet. By reversing the electric current, the electromagnet will attract the permanent magnet.
Note that if the permanent magnet is free to rotate, it will probably spin around so that it has the opposite pole next to the electromagnet, and will be attracted rather than being repelled.
The above is a primitive form of linear motor (http://en.wikipedia.org/wiki/Linear_motor). But you can also use a more conventional rotating motor (http://en.wikipedia.org/wiki/Electric_motor), and have it turn a pulley to move whatever it is that you wish to move.
If you have very high currents available, a rail gun (http://en.wikipedia.org/wiki/Railgun) creates its own magnetic field which can move a piece of copper - but they aren't very reusable.