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Magnetic field lines in a ring magnet

  1. Nov 28, 2014 #1
    Say if I magnetize a hollow cylindrical ring magnet by placing a staight current carrying wire along its axis. It will be magnetized with magnetic field lines running inside the cylinder clockwise or anticlockwise! So there will be no magnetic field lines outside the iron body? If I have a cylindrical hollow magnet or a magnet made by attaching two horse shoe magnets with magnetic field lines running along its length then, will there be any magnetic field lines outside the magnet? I think there will be because iron particles placed outside will get attracted to it. But how will these lines look?
  2. jcsd
  3. Nov 28, 2014 #2


    Staff: Mentor

    If you take a round bar magnet and drill a hole thru the axis of nort to south. It will still behave like a bar magnet but it's geometry is like a cylinder. The magnetic field lines circle around in north south plane it and through the drilled hole too.

    http://www.davidpace.com/images/stories/em/em2im5.png [Broken]
    Last edited by a moderator: May 7, 2017
  4. Nov 29, 2014 #3
    here, the domain run in circular fashion within the body. How will the magnetic field lines look?

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  5. Nov 29, 2014 #4
    This is the only orientation I have seen. If you stretch the ring into a tube the field lines would stretch into ovals across the length radiating around the circumference of the tube.
  6. Nov 29, 2014 #5


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    This is somewhat off-topic, but I have to mention it. I've never seen that particular field pattern before. It reminds me so much of a spider that I'm inspired to seek out other physics phenomena that have secondary associations and make an art project of it.
  7. Nov 29, 2014 #6
    Himanshu: The field around the wire is a Biot-Savart field and the ring will be magnetized with this field orientation. However, the Biot-Savart field extends to infinity so there will be a weak field outside of your magnet with the same orientation. The field is weak because of the high reluctance of air as compared to the iron ring.
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