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Several electromagnet questions

  1. Apr 11, 2009 #1
    Hello guys/gals

    I have a few questions regarding electromagnets that I'm hoping you can shed some light on for me. I don't know much about physics, magnets, etc. I am a career firefighter that is trying to build something requiring the use of electromagnets.

    1. I'm trying to have an electromagnet be able to repel another magnet (not electromagnet). When I electrically charge the electromagnet, does it automatically have a N and a S pole? Can I change what side is which? Also, is it constant which side is which when I charge it or does it change?

    2. If I put more current to the electromagnet, does the repelling force increase?

    3. What exactly are magnets made of? Can I weld other metals to it?

    4. Is there a good place online to purchase magnets/electromagnets? I'm looking for about 2" diameter and 1" or 2" height cylinder.

    5. Is there any material that can cancel the magnetic force? Example, some kind of material that I can wrap around the electromagnet and magnet to cancel out the magnetic field so it doesn't affect other things around it?

    Hopefully everything made sense. I'm sure I'll think of a few more questions in the near future.

    Thank you so much for any help you can provide.
  2. jcsd
  3. Apr 11, 2009 #2


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    Welcome to PF, 6fthook. (Honestly now, isn't that an exaggeration? :uhh:)
    The polarity of an electromagnet is determined by which way the current is flowing. Swapping positive and negative connections changes the field orientation.
    Increasing the electrical input does indeed strengthen the field, but be careful not to overload your windings.
    Lots of different materials can be used to make magnets. The easiest and cheapest is iron or steel. Other metals can be welded to it.
    EftonScience (formerly Edmund Scientific Co.) used to sell an electromagnet of approximately the size that you specified. It ran on 2 'D' cells and had a 500lb. lifting capacity. I haven't seen a catalogue in decades, so I don't know if it's still available.
  4. Apr 12, 2009 #3


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    There isn't a way to shield against magnetic fields like you can with electric fields. The best you can do is have a high mu material wrapped around the magnet to try and concentrate most of the field in the high mu. Another method is to have a second magnet that approximately cancels out the original magnetic field.
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