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Homework Help: Potential difference problem

  1. Feb 15, 2005 #1
    Two parallel plates having charges of equal magnitude but opposite sign are separated by .12 m. Each plate has a surface charge density of 36 nC/m^2. Determine the potential difference between the plates.

    I have to admit I am at a bit of a loss on how to answer this
    (lettings S represent the integral sign)
    I know Delta V = -SEds
    and that E is constant so
    Delta V = -ESds so delat V = -Ed
    but I am not sure how to find E, I know sigma =Q/A
    and I dont see how Gauss' law could really work here

    any light someone can shed would be greatly appreciated.
  2. jcsd
  3. Feb 15, 2005 #2
    Pretty classic problem. Assume the plate is infinite and make a cylindrical gaussian surface whose length is perpendicular to the face of a sheet: Illustrated in better detail here

    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.html#c2 Just remember that through the top and bottom of the cylinder flux equal to EA comes out, so the total flux is 2EA.
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