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How can I find the electric field above an infinite sheet?

  1. Sep 16, 2014 #1
    1. The problem statement, all variables and given/known data
    A square insulating sheet 75.0cm on a side is held horizontally. The sheet has 7.40nC of charge spread uniformly over its area. Calculate the electric field at a point 0.240mm above the center of the sheet.

    2. Relevant equations

    [itex]\Phi[/itex] = 2EA
    E = [itex]\sigma[/itex] / 2[itex]\epsilon[/itex]

    3. The attempt at a solution
    With the formulas above I managed to find that [itex]\sigma[/itex] = 1.316 * 10^-8, but I do not know that [itex]\epsilon[/itex] represents or how to find it. I cannot find the electric field until epsilon has been found.
  2. jcsd
  3. Sep 16, 2014 #2


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    Science Advisor
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    [itex] \epsilon [/itex] is the dielectric constant of vacuum (usually written as ## \epsilon_0 ## ). It is a constant that you can look up.
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