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Einstein-de Haas Experiment: Magnetic Dipole Moment Alignment

  1. Jul 30, 2011 #1
    So, you surround a ferromagnet with a solenoid.
    Run current through solenoid to create B field withing.

    2 Questions:

    1:Why do the magnetic dipole moments in the ferromagnet "align" with the magnetic field of the solenoid? Doesn't lenz's law say that the magnetic field within the ferromagnet will "oppose" the introduced B field in the solenoid.

    2:Consider a birds eye view of an electron orbiting a nucleus in the clockwise direction. Is the opposition of the Magnetic Dipole Moment (MDM) and the Angular Momentum vector of an atom/electron caused by the fact that L will point down due to the right hand rule and because convention says that MDM will point up because we use the CURRENT (flow of positive charge, not -ve) and the right hand rule, causing the MDM to point up?

  2. jcsd
  3. Jul 31, 2011 #2
    1. Lenz's law is about induced currents (which has to do with dB/dt). There are magnetic dipoles in ferromagnetic material that would already be in the material before the B field is applied. The torque on a magnetic dipole m is mxB, which would, for an off B-field axis magnetic dipole, cause angular acceleration toward alignment. The B field aligned magnetic dipole is in the lowest energy alignment state.

    2. Yes
    Last edited: Jul 31, 2011
  4. Aug 1, 2011 #3
    Cheers : )
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