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The work done by two electromagnets

  1. Sep 2, 2011 #1
    The "work" done by two electromagnets

    It has been said that magnets attract and repel by involving the use of electric fields.

    If so, how does the shape of the electric field change when an iron bar is magnetized?

    I would presume that the relative motion of the magnet as a whole is not what causes the magnetization because one can measure a magnetic force between two magnets held apart from each other. So the magnetic force must somehow exist even for magnetic dipoles that are stationary in relation to one another.

    It is not as if the force field around the magnet functions as an electric dipole having - and + ends! Where does one see electric field lines sticking out of a magnet to explain "magnetic" attraction and repulsion? Doesn't the magnetic field in fact derive its origins from electric currents that exist right angles to the magnetic field lines? Any current induced by magnetic fields would of course be induced only at a right angle to the magnetic fields, with no preferred direction along (or even at right angles) to the magnetic field as these motions would be exactly canceled (due to being induced within in a current "loop"), so generation of such currents obviously cannot explain acceleration of magnets along their field lines either.
  2. jcsd
  3. Sep 3, 2011 #2


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    Science Advisor

    Re: The "work" done by two electromagnets

    By whom?
  4. Sep 3, 2011 #3
    Re: The "work" done by two electromagnets

    Magnets use a magnetic field. Charged bodies use electric field.
  5. Sep 3, 2011 #4


    Staff: Mentor

    Re: The "work" done by two electromagnets

    I haven't heard that either.
  6. Sep 3, 2011 #5
    Re: The "work" done by two electromagnets

    I posted it because it was strange to me and didn't quite make sense. I am actually surprised hear that most people did not hear about this claim.

    I have read the line "magnets do no work" so many times, and yet I have heard contrary things too.

    Another other statement goes along the lines of "the electric field is what does the work" or "(time-varying) electric field". I can't help but try to visualize what the vector field of such a field would look like, and there would seem to be no reason why such a field, if it would really do what these people claim, would have a pattern any different than those of a magnetic field. Yet, from my understanding, the electric field is a totally different shape than the magnetic field. So using "(time-varying) electric fields" to explain magnetic attraction and repulsion didn't quite make sense to me.
  7. Sep 3, 2011 #6


    Staff: Mentor

    Re: The "work" done by two electromagnets

    Magnets certainly do work, that is how a generator works for example. E.g. a turbine does work on a permanent magnet and the magnet does work on the circuit.

    Now, a magnet cannot do work on a free charge, perhaps you were misinterpreting statements to that effect as more general statements?
  8. Sep 4, 2011 #7
    Re: The "work" done by two electromagnets

    In the case of artificial electromagnets with coil shape, the work is done by electric field supplied by battery or other electric supply in order to maintain electric current that is reduced by Lorentz force by magnetic field of the other magnet.

    In another case of electromagnets originated from quantum spins of materials, the work cannot be attributed to electric field because spin electric current cannot change.

  9. Sep 4, 2011 #8
    Re: The "work" done by two electromagnets

    If EM radiation is produced by the spontaneous aligning of quantum spins, is the mass of the whole reduced relative to the mass of the parts, or do the mass of the parts also decrease by amount accounting for the reduction of the mass of the whole? I'm not sure, but if the latter were the case, then the mass of each electron would reduce as a result of the alignment, and yet the mass of the electron is a fundamental constant.... so I don't know how to reconcile that yet.
  10. Sep 4, 2011 #9
    Re: The "work" done by two electromagnets


    In my latter case of magnetism by spin, energy in material is volume integral of HM where H is intensity of magnetic field and M is spontaneous magnetic flux density by material with spin. We can interpret energy balance by this quantity though it does not seem to be reduced to electric field.

    Last edited: Sep 4, 2011
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