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Homework Help: Insulating cylinder

  1. Jan 19, 2006 #1
    Here's the problem:

    An infinately long cylinder of radius R has a volume charge density that varies with the radius as p = p0(a-r/b) where p0, a and b are all positive constants amd r is the distance from the axis of the cylinder. Use Gauss' law to determine the magnitude of the electric field at r<R and r>R.

    here's my logic for r < R:

    E = k * int[p*dV/r] = k*p0*int[(a-r/b)*dV/r]
    -Then sub in V=Pi*r^2*L (solved for r and integrate wrt V)

    but what is this L if it's infinate. Also what is the difference being inside or outside of the cylinder? is it just the limits of integration (ie 0-R, or R-r)?

  2. jcsd
  3. Jan 19, 2006 #2


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    Science Advisor
    Homework Helper

    Symmetry tells you the electric field is radial and azimuthally symmetric. Gauss' Law relates the flux of electric field through a closed surface and the amount of charge contained therein. Rethink your approach! :)
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