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Homework Help: Electromagnetics coulombs law and field intensity

  1. Sep 17, 2012 #1
    1. The problem statement, all variables and given/known data
    The circular region, ρ < a, z= 0, carries a uniform surface charge density ρ ( subscript s). Find E at P(0,0,h), h > 0.

    2. Relevant equations
    Coulombs law
    Field of a line charge and field of a sheet charge.

    3. The attempt at a solution
    I'm not sure what they are asking for , but my attempt I used the equation for a field of a sheet of charge cause it's the only one provided in the Homework that contains the ρ (subscript s).

    It says E at point (0,0,h) so I'm guessing since its at z = 0 then the vector would be (0,0,h-0). Resulting in my result of

    E = (ρ(subscript s) / 2ε ) (0,0,h)

    Im not really sure what I'm supposed to be finding
  2. jcsd
  3. Sep 17, 2012 #2
    Okay so I get a little bit, I'm looking for the E of a circular region with the radius of ρ ?
  4. Sep 17, 2012 #3


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    Staff Emeritus
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    Hello Alwaysprolol. Welcome to PF !

    (Use the X2 and X2 icons for superscripts & subscripts.)

    Using the E field for an infinite sheet gives the wrong answer.

    Do you have an expression for the E field along the axis of a ring of charge?
  5. Sep 17, 2012 #4

    Unfortunately, I was not given one. The professor has given us only equations for E of a line charge and a sheet and I'm not quite sure how to utilize them in this question since its asking for the E in a circular region
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