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How do I contain a magnet's magnetic field?

  1. Jan 13, 2008 #1
    I want to buy a Neodymium Iron Boron magnet (N45 or higher), the ones with a very strong pull force. I want to keep it somewhere safe when I'm not doing experiments with it. Is there a way to contain the force so my metals don't fly half way across the room smacking my face along the way? Maybe a box I can put it in? Thanks.
     
  2. jcsd
  3. Jan 13, 2008 #2

    DaveC426913

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    OK, they're not exactly that strong. :rolleyes: The strength of a magnet drops off as the cube of the distance. You don't need to block the magnet so much as you just need some distance. If the magnet has several inches separating it from anything coming close (say, by putting it in a medium-sized box) nothing will be unduly attracted to it.

    But that being said, the one thing that best "blocks" magnetism is soft iron. The magnetic field will tend to follow the iron rather than passing through it. However, your implementation is a bit usual - usually you're trying to keep magnetism from affecting something inside a box. i.e. the magnetic field will go around the outside of the box rather than thorugh it.
     
    Last edited: Jan 13, 2008
  4. Apr 3, 2009 #3
    Just reading through. Just noticed one thing that bothered me. Magnetism is an inverse square law, so it wouldn't be the "cube" of the distance. moving two meters away would mean 1/4 of the original field strength.
     
  5. Apr 3, 2009 #4

    DaveC426913

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    Can you please supply a citation for this? I think it's the cube but I'm willing to be corrected.
     
  6. Apr 3, 2009 #5
    A monopole field will scale as inverse square. So how will the long range field of two monopoles (= 1 dipole) scale?
     
  7. Apr 3, 2009 #6
    I am sorry. It appears as though I was thinking about the magnetic monopole, wherever that may exist. The magnetic field strength decay has an inverse cube proportionality. Excuse me for the mistake.
     
  8. Apr 3, 2009 #7
    I don't remember the web-site where I purchased 8 large NIB magnets, but I do remember how they shipped them.

    When I opened the cardboard box, there were 2 U-shaped/square soft iron "shields' that I had to remove(easily), and the NIB's were inside embedded in some type of styrofoam mold.
    I'm sure part of this was due to some postal regulation, but I was impressed.
     
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