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Magnetic Poles

  1. Sep 25, 2005 #1
    Am I correct in assuming that if the distance between two poles of different magnets is halved, then the force of repulsion (or attraction) will increase while the attraction (or repulsion) will decrease? If the distance is halved, isn't the force quadrupled?
  2. jcsd
  3. Sep 25, 2005 #2


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    Magnetic Field strength decreases far from the source.

    If the source magnet has poles "close" to one another
    compared to width (ie, small button or disk magnets),
    then the field drops off roughly as 1/r^3 (not 1/r^2).

    If the poles are very far apart compared to their width,
    (5"x1" bar magnets have poles only about 3" apart)
    then their field drops off roughly as 1/r^2 .

    A little button magnet in a uniform B-field will
    experience almost zero (intrinsic) net Force,
    but in a spreading field will experience net Force
    proportional to the the distance between poles.

    Permanent Magnets (the ones filled with metal)
    respond in subtle ways to being in a B-field ...
    becoming temporarily stronger than usual,
    with extra strength proportional to external B.

    So, with small non-saturated disk magnets,
    you could get F ~ 1/r^6, (7 in special cases)
    but with "well-isolated" magnetic poles that
    are almost saturated, F could go as 1/r^2 !

    Physics is about *modelling* Nature,
    whatever the behavior is that we observe.
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