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Pulsed Point Dipole

  1. Feb 11, 2010 #1
    In Jackson's E&M book, he talks about using the following charge and current densities to demonstrate causality in the coulomb gauge.

    [tex]\rho (\vec{r},t)=\delta(x)\delta(y)\delta'(z)\delta(t)[/tex]

    since they represent a point dipole flashing on and off at time t=0. I understand the 'flashing' aspect since the densities are only non-zero only at t=0. What I don't understand is why this represents a point dipole... why is the [tex]\delta'(z)[/tex] primed in the charge density? and likewise with the [tex]\delta'(t)[/tex] in the current?

    Any thoughts?
  2. jcsd
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