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Dipole Moment Integration Question

  1. Feb 22, 2014 #1
    In "An Introduction to Electrodynamics", Griffiths gives the following equation for the dipole moment: [itex]p=\int r' \rho(r') d\tau'[/itex]. My question is, in general, what volume am I integrating over? It seems a bit arbitrary to me. I assume I'm integrating over whatever volume is enclosing the charge density [itex] \rho(r') [/itex]?
  2. jcsd
  3. Feb 22, 2014 #2


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    You are summing over all elements of volume ##\small d\tau'## in all of space. However, there is no need to integrate over those parts of space where the integrand is zero. So, you are correct - you only need to integrate over regions where there is some nonzero charge density.
  4. Feb 22, 2014 #3
    That makes sense to me. Thanks!
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