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Magnet poles ?

  1. Mar 4, 2004 #1
    Let’s say I make ball (sphere) out of permanent magnet material.
    Where will be N/S poles, will they take fixed position or, as I think, position wont be fixed.

    p.s. same for magnet ring
    Last edited: Mar 4, 2004
  2. jcsd
  3. Mar 4, 2004 #2
    I have a bunch of NdFeB sphere magnets in various sizes. All the time the poles are on the opposite ends, and they don't move. It wouldn't be permanent if they did move. It is possible to make them not be on opposite ends, but I never seen a sphere magnet like this.

    As for ring magnets, the poles are usually on the flat ends, but not always.
  4. Mar 4, 2004 #3


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    Like the rings that contain and compress plasma in a TOKAMAK, they must be negative around the external diameter and positive around the internal, right?
  5. Mar 4, 2004 #4
    I'm not familiar with that, but I think something that compresses plasma would be an electromagnet and not a fixed magnet.
  6. Mar 6, 2004 #5
    I think EagleOne might be referring to something a little different.
    Not sure about this, but will share my thought experiment to see if it relates to his question:

    A hollow iron sphere is constructed, in halves, such that the "top" can be joined together with the "bottom" by circumferential screwing or welding.
    Before the "joining" a series of iron rods are welded on the inside of each half sphere, say, 9 for each half-sphere, and they point towards, but do not touch each other, in the center.
    Copper wire is wound upon each of these 18 rods such to enable an electromagnet for each rod, with the "north" pole facing outwards of the sphere and the "south" pole facing inwards at the center.
    After winding all the wires around the rods, a suitable battery source is connected to the wires.
    The "battery" is small enough to be contained within the closed sphere.
    The battery is turned on and the 2 halves of the spheres are joined.
    Conceptually, a "north" pole magnetic field will surround the sphere, creating, in effect, a monopole.
    But surely this cannot be, as there MUST be a "return" path(North-South) But the "return path is negated in construction due to design.
    So, what happens?
    I believe that this is the gist of his question.
  7. Mar 8, 2004 #6
    What I believe will happen in that situation is that you will have a south pole around the equator of the sphere. At any given point on the equator the magnetic field will not be as strong as the north poles because it is spread over a larger area than the north poles are, but the overall strength should be the same.
  8. Mar 8, 2004 #7
    Reading your post again, I think you are trying to distribute the iron rods all around evenly. In that case you create a very strong south pole in the middle of the sphere, which I belive will try to push itself out between all the north pole rods. You will probably end up with very weak north and south spots all alround the sphere.
  9. Mar 8, 2004 #8
    Fascinating, waynet.
    I wish I had the resources(though minimally required)to actually constructed the device as stated. I would love to see what actually happens.
    My gut feeling is that a) you are correct. Or b) that the design is such that it would create an impossible electromagnetic environment, causing the electromagnets to fail to function. Or c) that the "north" pole fields of each rod would actually terminate prior to contact with the inside of the outer sphere; instead sweeping back inwards towards the south pole, all the while entirely within the sphere, effecting no net magnetic charge on the outer part of the sphere whatsoever yet allowing the electromagnets to function fine.

    I suspect that c) would likely be the case. Perhaps someday I or others can perform this experiment to find out.
  10. Mar 8, 2004 #9
    I think A & C are the same thing, but I think a little bit of the magnetic field will slip out.

    Now What I was wondering if you had a long permanent rod magnet, and you coated the south side and the length of it with a superconductor so that only the north pole was exposed, what would that magnetic field look like? As far as I know a superconductor will perfectly reflect a magnetic field. I guess the south pole would have to push it's way back up the magnet, not something it would want to do.
  11. Mar 9, 2004 #10
    Yeah, your description of an experiment would be a good one, waynet.
    I would like to know the answer to the experiment you put forth.
    You know, you would think that SOMEONE would be willing to perform these types of investigations. After all, they do seem important.
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