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Homework Help: Electric Flux through an Infinite Plane

  1. Aug 9, 2008 #1
    1. The problem statement, all variables and given/known data

    A point charge 60 microcoulomb is located in the origin. An infinite plane located at z=5. What is the electric flux in the plane due to the charge?

    Q=60x10^-6 C at 0,0,0 (origin)
    z=5 (plane)

    Here, I consider the electric flux emanating from Q that passes through the z plane. Each radial electric field produced by the charge forms circle in the plane. I get the summation of each circle circumference's ratio with whole sphere to infinity.

    But I got 1/(2xepsilon) times 60microcoulomb = 30/e(epsilon). I know I did not got the right answer cause the answer must be the half of the charge. Any Idea of solving the problem? help.
     
  2. jcsd
  3. Aug 9, 2008 #2

    Doc Al

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    Staff: Mentor

    What do you mean that the answer must be half the charge? Gauss's law tells us that the total flux from the charge is [tex]Q/\epsilon_0[/tex]; what's half of that? (You've got it right.)
     
  4. Aug 9, 2008 #3

    Defennder

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    How do we use Gauss law here? It isn't an enclosed surface. I integrated it directly to get [tex]\frac{q}{2\varepsilon_0}[/tex].
     
  5. Aug 9, 2008 #4

    Doc Al

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    Staff: Mentor

    Just imagine one: A spherical surface surrounding the point charge. Clearly all "field lines" from one half of the sphere will pass through that plane.
    Nothing wrong with doing it the hard way. :wink:
     
  6. Aug 9, 2008 #5

    Defennder

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    Oh I see. Thanks.
     
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