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B Estimating magnetic field based on pull force

  1. May 8, 2016 #1
    I am trying estimate the approximate value in gauss of the magnetic field of a magnet I have based on its pull force, and I am wondering if anyone can comment on the validity of my method.

    I have tested the pull force of my magnet by weighing the heaviest object it can hold. I have also found data on another magnet made of the same material online. This data contains the pull force of the magnet in grams, and also the magnetic field in gauss. The two magnets are of similar shape, but obviously different masses.
    By comparing the pull force values of the two magnets, can I then estimate the magnetic field of my magnet? For example, if my magnet has half the pull force of the magnet online, will the magnetic field also be roughly half?

    (The two magnets are cylindrical, and I am thinking about the magnetic field value at the point in the center of the flat face at the end of the magnet - not at any distance away from the magnet)
  2. jcsd
  3. May 9, 2016 #2


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    Gold Member

    The attraction of some load is proportional to the magnetic energy density at the end of the magnet:

    Edens = ½*B*H [ J/m3 ]

    B = μ0 * H →

    Edens = ½*B*H = ½*μ0*B2

    So (roughly) F ≈ k*B2 , k is some constant. The B-value found is the mean flux density over the cross section area at the end of the magnet, not at the center or at the edge.

    "Roughly" because the magnetizing curves are not linear.
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