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Magnetic Field Alignment

  1. Nov 21, 2005 #1


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    Hi everyone,

    I have a question about the mechanics of the magnetic field alignment process. If you suddenly subject some iron filings to a magnetic field, they align along the magnetic field lines. I'd like to know how this happens step by step. I understand that the iron filings which were originally magnetically neutral need to magnetize and etc, although I can't seem to find a reason for that to happen.

    I also did I search about this topic before posting and I found a really interesting debate that may be somewhat related from 2004 (very old by web standards) on magnetic fields and work. The accepted fact was that the magnetic field cannot do any work on a charged particle (as stated in multiple textbooks). However... a fluctuating magnetic field certainly can, as seen in induction motors or generators of all kinds. It is somewhat more complicated by the fact that the magnetic field appears to be a 'secondary' field created through moving charges (i.e. fluctuating electric fields). Then there was an unrelated debate about magnetic dipoles I am also addressing in another thread. I think there was also confusion about work concepts. In anycase, my conclusion is that a magnetic field can certainly "do work" on another magnetic element the same way mass can "do work" on another mass element through gravity and a charge can "do work" on another charge element through the electric force. What do you think?
  2. jcsd
  3. Nov 21, 2005 #2
    Iron exibits ferromagnetism, and a ferromagnetic material under an external magnetic field develops a strong magnetic dipole moment. so now there we have a magnetic field and a dipole, and force will certainly come along.
    I'd not say that the magnetic field is a secondary field. As you said moving charge create magnetic field true enough, but also there we have some magnetic materials exibiting magnetic fields of there own like a bar magnet or a lodestone( i can't think of of anything else right now). Also as you might know changing magnetic field also generates electric field, as in EM wave propagation.
    It certainly do work on a magnetic element.
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