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How to calculate the magnetic dipole moment?

  1. Jun 7, 2013 #1
    How to calculate the magnetic dipole moment?!?!

    Does anyone out there know how I can calculate the magnetic dipole moment of a simple bar magnet?
    Or any kind of magnet?

    Without using this formula: [itex]\tau[/itex] = μ x B
  2. jcsd
  3. Jun 7, 2013 #2
    I think that I need to figure out the pole strength (m1, m2) of the magnet and them figure out the moment.

    I think, the magnetic dipole moment is μ = md
    d= separation between the two poles?

    I'm not sure though...
    IN FACT, how can anyone calculate the pole strength in A.m?
  4. Jun 8, 2013 #3


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    Do you mean calculate from first principles? I don't think that's easy. At zero temperature, if there are no grain boundaries, you could probably add up all the dipole moments from all the atoms. If it's ferromagnetic, I think they line up.

    At higher temperature, you need to calculate the occupancy of aligned versus non-aligned spins. I guess it takes a Boltzmann distribution for each atom, but they are coupled so you need some kind of mean field approximation or something.

    But if there are grain boundaries, that kinda screws up everything.
  5. Jun 8, 2013 #4
    Well would anyone calculate the magnetic moment and the magnetic pole strength?
    μ = ?
    m1= ?

    What way can I figure out the magnetic moment/magnetic pole strength.
  6. Jun 9, 2013 #5

    Jano L.

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    You can measure the force the magnet exerts on current loop of known magnetic moment, use the formula for magnetic force to determine the magnetic field B the magnet produces, and then calculate what poles are needed to produce such field.
  7. Jun 9, 2013 #6
    The magnetic field B is already given.
    I only need to calculate the moment.
  8. Jun 10, 2013 #7

    Jano L.

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    In what way is the magnetic field given?
  9. Jun 10, 2013 #8
    The magnetic field is measured by an instrument.
    Its at 0.3426T
  10. Jun 10, 2013 #9

    Jano L.

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    At which point?
  11. Jun 10, 2013 #10
    At point r.
  12. Jun 11, 2013 #11

    Jano L.

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    Can you post a drawing? I do not know where "r" is.
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