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Homework Help: A question on electric fields

  1. Mar 22, 2008 #1
    What is the field near a square metal plate (with infinitesimal thickness)

    The answer is E = [tex]\sigma[/tex] / [tex]\epsilon[/tex]

    where [tex]\sigma[/tex] = Charge per unit area

    [tex]\epsilon[/tex] = relative permeabily

    Please help me to derive this result. using coulombs and then gauss' law
  2. jcsd
  3. Mar 22, 2008 #2
    What will be the first step?
  4. Mar 22, 2008 #3
    For coulomb

    [tex]\int[/tex] dE = k [tex]\sigma[/tex][tex]\int[/tex] 1/r^2 dA

    Im getting

    E = [tex]\sigma[/tex] [tex]\pi[/tex] / 8 [tex]\epsilon[/tex]

    The symbolys are multiplying not tothe power of. This result is wrong
  5. Mar 22, 2008 #4
    I didn't understand how did u get that answer.
    newayz, try using gauss theorem... what is the Gaussian surface here?
  6. Mar 22, 2008 #5
    no i want to use colomb
  7. Mar 22, 2008 #6
    K, then you have take a disc with infinitesimal width, find electric field due to it, and integrate for radius = 0 to infinity(coz the sheet is infinite)
  8. Mar 22, 2008 #7
    i know
  9. Mar 22, 2008 #8
    im just not getting the right ans
  10. Mar 22, 2008 #9
    k, tell me what is electric field at a distance x from the infinitesimally wide disc of radius r ?
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