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Magnetic Forces

  1. Apr 23, 2009 #1
    I'm wondering about general magnetic forces, specifically the behavior of unmagnetized ferromagnetic materials in a magnetic field. I.e., a simple bar or electromagnet picking up an unmagnetized piece of iron.
    Are there formulas to explain this behavior? The lorenz force equations by themselves don't help me here.
  2. jcsd
  3. May 2, 2009 #2
    I don't know the formulas for the force exerted, if that's what you want, but I can explain why it happens. The iron becomes temporarily magnetized by the magnetic field, so it's (temporarily) like two magnets pulling on each other.

    This is sort of analogous to the way dispersion works for electrostatic forces (i.e. rubbing a balloon to make it charged and then sticking it to the uncharged wall).
  4. May 2, 2009 #3


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    Welcome to PF!

    Hi MonkeysPass! Welcome to PF! :smile:
    A magnetic field, of course, only exerts a force on moving objects.

    The moving objects in the material are electrons in circular orbits.

    The magnetic field exerts a force on each orbiting electron. And this is the Lorentz force

    In most materials, the orbits are at random (and stay that way), so the forces are also random, and cancel out on average.

    But for some materials (ferromagnetic, etc), the orbits align, and the forces all act in the same direction, and so the material moves. :wink:
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