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Easy question, magnetic poles

  1. Mar 11, 2005 #1
    What determines a magnetic pole? Everyone has known sence elementry school that on a bar magnet (and the earth) have North and south magnetic poles... my question, what make a (bar magnet) that way? If I were to cut a bar magnet in half(between the poles) would I have one magnet that was North and one that was South? and if not, what would make them change to them both haveing North and South poles?
  2. jcsd
  3. Mar 11, 2005 #2
    isn't north positive and south negetive, or something
  4. Mar 11, 2005 #3
    Magnetic Fields are continuous loops

    If you cut a bar magnet in half, you will have 2 bar magnets that have north and south poles. This is a key part of electromagnetism. The magnetic fields
    are continous loops, which when you cut the bar magnet in half, you just make the loop smaller for each piece. As for why permanent bar magnets are the way they are, I believe that quantum effects play a part.
  5. Mar 11, 2005 #4
    Yes but there is something in it that determines what would and wouldn't be compatable with other poles on other magnets. and also... can a magnet's magnetic field be increased?
  6. Mar 11, 2005 #5
    All magnetism results from rotation or motion of charge. In a permanent magnet this is the alignment of the spin properties of the electrons in the material. For a bar magnet this can be visualized as a current circulating around the long axis of the bar. Now look down one end. The current is clockwise. Look at the other end counterclockwise. If you use the the convention of positive current (opposite to electron flow as electrons have negative charge) then counterclockwise is north, clockwise is south. Hope I got that right. :biggrin: Anyway one is north the other south. Now when you break the bar in half what happens?
  7. Mar 11, 2005 #6
    do you mean when you rub a magnet over another unmagnetised bar of metal, the direction you rub it in defines the direction of the magnetic flow
  8. Mar 11, 2005 #7
    Magnetizing an iron rod with a permenent magnet works something like this. Throughout the structure of the iron (or steel and some alloys) are regions called domains. The entire rod is divided up into them. The spins of the electrons responsible for ferromagnetism tend to "cooperate" within a domain, for quantum mechanical reasons, iirc. In an unmagnetized rod the magnetic fields of the domains are randomly oriented. There is a property of domains such that they tend to have "memory" of their individual allignments. By moving a magnet along the rod (you don't actually have to rub it) you "drag" the domains to a common alignment. This is a simplified explaination and I'm not a magnetic materials expert, but that is the basic idea.
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