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I Force on a ferrous object inside a non-uniform magnetic field

  1. Jul 20, 2016 #1
    Hello everyone!

    I want to know how to compute the force applied on ferrous inside a non-uniform magnetic field, to make it easier, let's assume that the field direction is constant, and the magnitude decreases linearly.

    Now, I know that ferromagnetic material inside a magnetic field will become magnetized, and once he become magnetized, I can compute the induced currents on the surface and inside the matter(curl of M, and Mxn, where M is the magnetization), and therefore I can use Lorentz law to compute the force.
    Is that right to do this?

    I saw that usually engineers using programs like FEMM to solve such problems, and I try to figure out how to solve it analytically

    simple examples:
    http://uzzors2k.4hv.org/index.php?page=magneticlevitation - the force applied should be similar to this:

    simple problem:
    assume we have an air-core solenoid produces a magnetic field(instead of the iron-core in the example), I want to know what is the minimum number of turns or the minimum current I need to pull a given iron cylinder (given distance from the solenoid, and given mass, and for simplify the problem I can assume that the cylinder is right in the symetric axis of the solenoid)
    Last edited: Jul 20, 2016
  2. jcsd
  3. Jul 20, 2016 #2
    OK, few thougths...
    1.my first thougth about induced currents and lorentz law will not work here
    2.If I will use the magnetic potential: μm=0.5⋅μ⋅H⋅H
    I can compute the force by F=-∇μm

    H is function of z, so F is also function of z. If I omit ellastic forces on the iron cylinder(can I? maybe tension?)
    I will get: F=-∫∇μm between z1 and z2(z2-z1 is the length of the cylinder)

    what do you think?
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