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Questions on ferromagnetism and attraction

  1. Jun 24, 2009 #1
    I have questions about magnetic attraction in both conceptual and application. I am not a physicist (medical background) so I may have insufficient understanding of the concepts involved, but any clarification would be helpful.

    Suppose I have a field source, such as a permanent magnet, and a ferrous object is rigidly held at a fixed distance from the source. I want to know how to calculate the force of attraction for a particular material and particular shape (i.e. a cube of iron). As the iron approaches the source, it is pulled in with increasing force up to the point of contact.

    My current understanding of ferromagnetic materials is that, when exposed to a field, (1) permeability greater than that of a vacuum (or air as the case may be) allows flux to be ‘conducted’ through the material. At the same time, (2) the ferromagnetic material begins to act a magnetic sources itself, and (3) at a point of saturation can channel no greater amount of the flux.

    As the distance between two magnets increases the pull should increase in an inverse squared relationship, but the “magnetic strength” of the iron is increasing as well so is there a different (cubic or other) relationship in the case of ferromagnets? If so, in the case of “saturation” does the regular inverse squared force relationship resume? The real question then is, given enough information about the materials involved, are there mathematical formulae to represent the interaction of iron and magnet, namely force?
  2. jcsd
  3. Jun 24, 2009 #2

    I'm not anywhere near current on magnetic designs and calculations, but I'm pretty sure that's quite a complex undertaking.

    You can take a look at Wikipedia http://en.wikipedia.org/wiki/Permanent_magnet#Calculating_the_magnetic_force
    for some ideas....

    Permanent magnets come in dozens if not hundreds of materials and strengths and shapes, and likewise "ferrous" describes a wide range of materials as well. I'd guess this kind of question is answered in tables of magnet types and ferrous material relationships where results have been experimentally measured rather than theoretically calculated. Maybe somebody knows the latter; I've never seen such theory.
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