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Homework Help: Problem on Gauss's Law

  1. Oct 13, 2008 #1
    1. The problem statement, all variables and given/known data
    The spherical region a < r < b carries a charge per unit volume of [tex]\rho[/tex] = A/r, where A is a constant. At the center (r = 0) of the enclosed cavity is a point charge q. What should be the value of A so that the electric field in the region a< r < b has constant magnitude?

    The answer says A = q/(2pi a2)

    2. The attempt at a solution
    I drew a sphere with radius r as a Gaussian surface.
    My work is in the attachment.

    I got stuck from that point. I need help :!!)

    Attached Files:

    • gg.jpg
      File size:
      13.6 KB
  2. jcsd
  3. Oct 13, 2008 #2
    You go wrong in the second line, the right-hand side: the volume element is NOT [itex] 2\pi r dr [/itex], but....

    Otherwise, you got the right idea.
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