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Magnetic polarization

  1. Feb 23, 2009 #1
    I noticed that steel or iron objects tend to magnetically polarize in the earth's magnetic field. I am in Kazakhstan (northern hemisphere!! :-) The north pole of the magnetized objects seem to be at the top of the objects. Is this a coincidence? If not what is the explanation? Would it be different in the southern hemisphere?
     
  2. jcsd
  3. Feb 24, 2009 #2
    If you magnetize an object in the Earth's magnetic field, the north pole of that object will point towards Earth's North magnetic pole (which in turn, magnetically speaking is therefore a south magnetic pole). More precisely, it will be magnetized parallel to the lines of the earth's magnetic field. These usually are not parallel to the surface of earth, but point slightly downwards (to compensate for it, compass needles have a little weight on one side). The north pole of such object should therefore point downwards.
    Maybe you turned your object upside down =).
     
  4. Feb 24, 2009 #3

    clem

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    The B field of the Earth points down in the northern hemisphere and up in the southern hemisphere so the vertical component of the magnetization would be opposite.
    I agree with mp that you seem to have something backwards.
     
  5. Feb 25, 2009 #4
    Hi thank you for your replies.

    I have repeated the experiment with numerous compasses on a variety of objects (fire extinguishers, refrigerators, microwaves, radiators...) The metal objects were static and had not been rotated. To be sure that it was not just the earths magnetic field the compass was moved around the objects. In every case the north seeking pole of the compasses were attracted to the top of the metal objects and the south seeking poles attracted to the bottom.
     
  6. Feb 25, 2009 #5

    clem

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    I did not understand your first post. The metal objects are not permanently magnetized, but have induced magnetism caused by the Earth's magnetic field. Since this is directed downward in your northern latitude, the top of the metal object behaves like an S pole.
    It thus attracts the N pole of the magnet. All is well.
     
  7. Feb 25, 2009 #6
    Thank you. It's good to know the laws of physics are working properly in Kazakhstan :smile:
     
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