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How does a mgnet work?

  1. Apr 23, 2008 #1
    Is there any evidence that particles are exchanged to mediate the magnetic force?

    If there is how do these particles cause a one magnet to cause motion in a
    particular direction for another magnet?

    If there are no particles mediating this reaction how would a field line exert the
    force?

    What are magnetic fields made of?
     
  2. jcsd
  3. Apr 23, 2008 #2
    No, particles are not exchanged in any way.

    No D=

    In a raw piece of metal, domains of motion are all in disorted order. Magnet generates a magnetic field that aligns all those domains in one direction, thus forcing them to move towards the magnet.

    Out of magnetic fields


    More info about magnets can be found here: http://coolmagnetman.com/maghow.htm
     
  4. Apr 23, 2008 #3
    According to quantum electrodynamics, the magnetic force (and the electric force) is mediated by virtual photons. The theory makes very accurate predictions. See http://en.wikipedia.org/wiki/Precision_tests_of_QED

    The evidence for virtual particles is indirect because an individual virtual particle cannot be observed. According to the theory, what we see are the aggregate effects of an infinite number of virtual particles. From a philosophical standpoint, one can argue that this does not really prove that virtual particles exist. And that is correct. It doesn't really prove it. But the theory works very well and will continue to be used until a better one comes along.

    Magnetism is a fairly complicated force. You can find a tutorial here: https://www.physicsforums.com/showthread.php?t=95523

    Photons (maybe).
     
  5. Apr 23, 2008 #4
    That's the classical theory of electromagnetism. This is the quantum age. ;)
     
  6. Apr 24, 2008 #5
    Thank you everyone for your time. I have checked out the links and read everyones comments. I would like to ask some follow up questions.
    1. Am I correct in believing that the dominantcurrent theory says that the mediator of the electromagnetic force is the virtual photon?
    2. Is the transmission of virtual photons supposed to be the source of magnetic field lines?
    3. How is it that virtual photons are thought to cause something to move toward something else?
    4. Is it correct to say magnetic domains within a material are caused by groups of atoms that have aligned their electron spins? What is meant by saying that the electron spins are aligned?

    I appreciate knowing when something is suggested by direct evidence and when it is implied by indirect evidence and when we just don't know.
     
  7. Apr 25, 2008 #6
    Yes.

    Yes. But one shouldn't think of the photons as traveling along the field lines. A virtual photon travels from one charged particle to another. The field lines are a way of representing the classical field. They are only indirectly related to the virtual photons.

    One charged particle emits a virtual photon. Another charged particle absorbs it. In the process, the particles exchange some energy and momentum, and this causes a change in motion.

    You can find a good explanation of the theory in the book "QED" by Richard Feynman.

    Yes.

    "Spin" is the intrinsic angular momentum of the electron. The electron has some properties that are similar to what you would expect if it were a little spinning ball. (Purists will tell you that it's not really a spinning ball. It just has some properties that are like a spinning ball.) Anyway, if the spins are aligned, that just means that the electrons are spinning the same way. (Purists will tell you that's not the right way to think about it, but that's simplest way I can think of to explain it.)
     
    Last edited: Apr 25, 2008
  8. May 14, 2008 #7
    Phlogistonian,

    I could see momentum pushing but how can it pull?
     
    Last edited: May 14, 2008
  9. May 14, 2008 #8
    Good question. That's never been clear to me, either. I remember wondering about that, but when I learned QED, I got so bogged down in learning the details of the mathematics that I forgot about it. QED is very complicated. :yuck:

    It bothers me that I don't know this, so I'll look into it, but it may take me days or weeks to figure it out. Maybe someone who understands it better can answer your question.
     
  10. May 15, 2008 #9
    Please excuse my laziness in research before asking this, but is magnetism associated only with electrons, or can other charged particles exhibit the magnetic phenomenon, such as the proton, etc...?
     
  11. May 15, 2008 #10
    Every charged particle with spin possesses an inherent magnetic field. And every charged particle in motion produces an additional magnetic field from the motion.
     
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