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Where does the force come from?

  1. Jun 26, 2011 #1
    We have a circular non conducting ring placed in a uniform magnetic field with its direction perpendicular to the plane of the ring. There is a charge present on the ring. The field changes with a rate dB/dt. By lenz law we know that the ring will start rotating to form a current that will oppose change in B.

    But if we apply basic rules of physics - Where does this force required to move the ring come from?:eek: there is only magnetic field which cannot affect a rest charge.
  2. jcsd
  3. Jun 27, 2011 #2


    Staff: Mentor

    By Faradays law, if you have a changing B field this will induce an E field. So it is not correct that there is only a B field, there is both E and B.
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