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Shaping a magnetic field

  1. Jul 26, 2010 #1
    Hi all,

    I have been playing around with some neodymium magnets recently and have found that although they are indeed very strong the 'range' of the magnetic field is not very large.

    So I was wondering if there is a way to shape the magnetic field so that the magnets would attract/repel each other from a greater distace.

    Hope I've made myself clear! :)

  2. jcsd
  3. Jul 26, 2010 #2
    Not in any useful sense.

    You can use soft iron to 'conduct' the magnetism much like a wire conducts electricity, but there's no way to get a 'focussed' magnetic beam such as I imagine you are thinking of.
  4. Jul 26, 2010 #3
    Not really trying a 'beam' more like a 'stretched' field. I read somewhere that you can use sheets of aluminium or copper to do this.
  5. Jul 26, 2010 #4
    Assuming that you understand that a magnetic field is not emissive(in the sense of a monopole) a magnetic field must have a return path to exist(as we currently understand; could change)

    Because of this, options to "stretch" the field is limited, and requires additional components.
    Even with additional components, the "stretch" is severely limited.
  6. Jul 26, 2010 #5


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    Aluminum or copper will only work for alternating magnetic field.

    If you have a permanent magnet, the only thing that will achieve this sort of effect is a superconductor. A superconductor does not allow magnetic fields to pass through it (well, Type I doesn't, with Type II it's a little more complicated, but anyways...). So if you have a superconductor tube, and you put a magnet at one end of it, near the other end, it will be as if the magnet is right there.
  7. Jul 27, 2010 #6
    Does connecting two permanent magnets with a soft iron rod extend the field as if it were a single magnet as long as the overall length?
    Would the rod being a different diameter make a difference? (assuming identical size magnets)
  8. Jul 27, 2010 #7


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    If you represent the magnet as a pair of magnetic monopoles (yes, they aren't real, but it works as a mathematical trick) then yes, something like that can be done to separate the monopoles further without altering their strengths.
  9. Jul 27, 2010 #8
    So is the best way to achieve a larger 'range' to shell out and buy bigger magnets? Or does this only increase the attraction/repulsion force?
    Last edited: Jul 27, 2010
  10. Jul 27, 2010 #9
    The range is infinite and magnetic fields are divergence free.

    If you want to pick up an iron ball from farther away, tape your magnet to a stick and then use that as an extension.

    If you want to "collect" field lines inside a solenoid for example, use an iron core.
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