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B How does Faraday's motor cause the wire to circularly move?

  1. Feb 16, 2017 #1
    Basically I'm not sure how the interaction between the circular magnetic field produced by the current in the wire and the magnetic field of the permanent magnet interact to cause the wire to move in circular motion. If someone could explain that I would appreciate it.
  2. jcsd
  3. Feb 16, 2017 #2
    It's all a function of the Lorentz force, and the fact that the resulting force is perpendicular to both the magnetic field and the current/charges. If you look at how the magnetic field lines run when they intersect with the wires, you'll see that the net result is a sideways force that then causes torque.

    That said, I just looked at the Wiki page of the homopolar motor, and they have this picture of the magnetic field lines:


    That picture looks really wrong to me. Why would the field lines not be radially symmetric around the battery? And, why would they "exit" at the bottom like that? The usual magnetic field of a circuit goes through the middle of the circuit, so I would imagine the field of the arrangement in the picture to have two of those.
    Last edited: Feb 16, 2017
  4. Feb 16, 2017 #3


    Staff: Mentor

    There is a small permanent magnet attached to the bottom of the battery. The field lines are symmetric about that permanent magnet.
  5. Feb 16, 2017 #4
    Aaaaah, that makes sense. They could have made that a bit clearer in the pic I think.
  6. Feb 16, 2017 #5


    Staff: Mentor

    I agree. The magnet looks like part of the battery the way they drew it.
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