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Homework Help: Electromagnetic Repulsion research

  1. Mar 15, 2009 #1
    1. The problem statement, all variables and given/known data

    I have made an electromagnet out of a 1 ft. iron nail, insulated copper wiring and a 1.5 D cell battery.

    My task is to use the electromagnet to repel a small, circular permanent magnet (1 in. dia., 1/4 in. thick)

    For some reason, I can only get the electromagnet to attract the permanent magnet. All of my research says that magnets, whether electromagnets or permanent, will attract when opposite poles connect and will repel when same poles connect.

    2. Relevant equations

    3. The attempt at a solution

    I've done everything I can think of to try and connect the same poles. I've tried flipping around the permanent magnet, connecting the permanent magnet to each end of the electromagnet, and switching the end of the wire connected the negative side of the battery to the positive side and vise versa.

    What can I do to make my electromagnet repel the permanent magnet!?!?!?!?

  2. jcsd
  3. Mar 15, 2009 #2
    Perhaps your electromagent is too powerful? Try reducing the number of coils. Or too weak even. Have you tested their relative strength qualitively, on a piece of iron say? Beyond that I have no idea, sorry.
  4. Mar 15, 2009 #3
    Hmmm...I don't think it's too powerful, if anything not powerful enough....It can barely pick up a few paperclips.

    Thanks for the suggestion though, I appreciate it.

    edit: I do have a TON of coils. The entire foot-long nail is covered. I always thought that coils x voltage = strength, so I used as many coils as possible to compensate for the 1.5 D cell battery.

    Maybe I'll try using less coils. I'll see what other responses I get here first though.

    Last edited: Mar 15, 2009
  5. Mar 15, 2009 #4


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    Your problem may be that the attractiveness of the iron with the permanent magnet over-matches the strength of the field you are generating with your battery. Maybe try a plastic rod? Or a bigger battery? Or more coils?
  6. Mar 15, 2009 #5
    That's actually what I thought was the problem at first, but I was told that it wasn't possible because magnets can't be attracting and repelling at the same time. But, maybe the person I asked didn't understand what I was trying to say.

    Thanks, I'll see if I can get a hold of a bigger battery.

    Also, what would a plastic rod be used for?
  7. Mar 15, 2009 #6


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    To wrap coils without an iron core, which may be the source of your problem.

    Or the center of a paper towel roll. Basically anything not magnetic.
  8. Mar 15, 2009 #7
    Oh...I thought you needed to have some kind of conductive core. I guess I'll give it a try.

    Also, is "amperage" simply battery strength? How do I increase amperage, increase battery strength? (I know it's a stupid question, but I'm a totaly newb to this kind of stuff)

  9. Mar 15, 2009 #8


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    Your D battery is pretty limited. 1.5 V in the partial-amp range. A car battery - 12 V and beau coup amps of current might be appropriate, but you need to worry about limiting the current with enough resistance so you don't hurt yourself or your coil doesn't burn if the wire is not thick enough. V = I*R

    Also more coils helps to increase the magnetic force you generate.
  10. Mar 15, 2009 #9
    I think you were right about the permanent magnet's attraction to the the iron nail exceeding the the strength of its magnetic field. I changed from a 1.5 D to 2 AAA's and I noticed that one side of the permanent magnet has a much stronger attraction to the electromagnet than the flip side. I think I just wasn't getting enough voltage through the electromagnet.

    Say I did use a car battery, what safety precautions would I have to take? Is there some way I could strip a cord and just plug the electromagnet into a wall socket?

  11. Mar 15, 2009 #10


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    You of course can do anything, but before you do anything DANGEROUS like wrapping AC cord and slamming a dead short into a wall plug or electrocuting yourself, ask yourself with AC current what kind of magnetic field does it create? Which end will be North? (How often a second?) See a problem with that?

    If you use a car battery or more batteries in series, figure what the resistance will be first so you know your current will be relatively safe. (A,B,C,D batteries in series will be safer than a car battery because they have natural limitations on what they can supply. They also discharge faster for a given load you may be sure.
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