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Derivation for Magnetic Field Due to Dipole

  1. Apr 13, 2009 #1
    I am looking for a reference (derivation) for this exact formula given for "the magnetic field due to a dipole [tex]\mu[/tex] fixed at the origin" :

    [tex]B=-\frac{\mu}{R^3}+\frac{3r(\mu\cdot r)}{R^5}[/tex]

    I don't really know anything about dipoles or how they are derived (I have only taken lower division E&M) so the [tex]\mu[/tex] has no meaning to me. It seems that this formula is derived from a vector potential [tex]A=\frac{\mu\times r}{r^3}[/tex] and I know that B = grad x A so it might help more to understand what this potential actually means as well as a good lesson on what is the dipole vector mu. Thanks.

    note:i'm having trouble rendering the tex so here is the formula in plain text:

    B=-u\R^3 + (3r(u dot r))\R^5 here i use small r for the position vector and R for the length of r and u stands for the greek letter mu for the dipole vector.
     
    Last edited by a moderator: Apr 13, 2009
  2. jcsd
  3. Apr 13, 2009 #2

    jtbell

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    Staff: Mentor

    I know it's in Griffiths's "Introduction to Electrodynamics." It's probably in other intermediate-level E&M textbooks such as Purcell or Lorrain & Corson.

    Griffiths does it as part of the general "multipole expansion" of the magnetic vector potential from a general distribution of current. You might try a Google search for something like "magnetic vector potential multipole expansion."
     
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