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Magnetism question regarding solenoids and shapes of their cores

  1. Jul 22, 2010 #1
    If I were to build a solenoid for the sake of making an electromagnet with a core shaped like the one below, would it create the desired effect?

    CRUDE! :tongue2: Cross-sectional view of my idea.

    What I'm asking is, would the inner edges of that gap (the sides closest to the center) be one polarity while the outer edge be another? I'm worried that having the iron core continue under the wire would hurt the field...

    Ideally one of the two rings in this top view would be "north" and the other "south"...

    Essentially, would the whole circular piece behave like a horseshoe magnet that is extended to become round?

    Thanks for any help and I'll be around the forums more as I traverse my path in physics
    (note: while I'm a student, this isn't homework o:) )
  2. jcsd
  3. Jul 22, 2010 #2
    If I interpret your drawing correctly: Yes, it would.
    It should be quite efficient. The field would appear across the gap only and be quite strong.
  4. Aug 6, 2010 #3
    As it stands now, I've found a calculator that optimizes the number of turns for the space given and wire gauge. It then uses that information and your input voltage to come up with the current, power, and it will estimate the "gauss at center". Now this is in the case of a simple electromagnet, not what I've designed above.

    Before the part arrives, how could I put the "gauss at center" unit into more understandable terms (like perhaps holding force)?

    If my design is as good as I hope, it may get a stronger holding force than the simple electromagnet calculator would indicate, however... I don't have a benchmark for what these numbers mean. I hope I've made myself somewhat clear, and thanks!
  5. Aug 6, 2010 #4
    It sounds like a simple calculator to give the magnetic field (which is measured in gauss) at the centre of a coil of wire,

    What you have is completely different. In fact it will probably be stronger by orders of magnitude than the calculator will indicate.

    It's possible to calculate these things but there are no simple formulae that I'm aware of for particular shapes and sizes - magnet design is not difficult - but it is complicated.

    Calculating the forces from the field strength is also quite complex.

    Your best hope is to simply make one and measure the strength. If it isn't strong enough use more turns / more current.
  6. Aug 6, 2010 #5
    It actually asks for the core size, so it might be a bit closer to what I'm doing, but not really. Thanks!
  7. Aug 6, 2010 #6
    Yes, I have a circular Alnico magnet just like your rings. For best performance, the cross-sectional areas of the two grey poles should be equal. The inner pole can be solid, not hollow.

    Bob S
    Last edited: Aug 6, 2010
  8. Aug 18, 2010 #7
    But does it NEED to be solid? There has to be that gap, unfortunately.

    Edit: By gap, I mean the open space in the center of the magnet.
  9. Aug 18, 2010 #8
    The gap between the inner and outer grey pole should be at least the width of the two poles shown in your diagram. [STRIKE]It may be filled with any non-magnetic material[/STRIKE]. Fill the gap with amp-turns of copper wire. The cross sectional areas (grey areas) of the two poles shown in your diagram should be equal. The inner pole may be hollow, as shown in your diagram.

    Bob S
    Last edited: Aug 18, 2010
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