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Homework Help: Electric Charge and Electric Fields

  1. Jun 6, 2006 #1
    Each quare centimeter of the surface of an infinite p;ane sheet of paper has 2.5 X 10^6 excess electrons. Find the magnitude and direction of the electric field at a point 5 cm from the surface of the sheet, if the sheet is large enough to be treated as an infinite plane.

    This is an odd problem and the answer is:
    226 N/C towards the sheet

    I understant why it is towards the sheet. I am guessing that since it is an infinite plane the 5 cm distance is unimportant.

    does this have something to do with the equation: E = 2*sigma / 2*Eo

  2. jcsd
  3. Jun 6, 2006 #2


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    Yes, that's the basic idea (except that the equation is 2 sigma /(2 epsilon_0).

    That's all there is to it.
    (you know how to calculate sigma, I assume. Just take the number of excess electrons times the charge of one electron divided by the 1 cm^2. Don't forget that 1cm^2 = 10^(-4) m^2).

    EDIT: I retyped the wrong equation by mistake. Sorry. It is of course sigma/(2 epsilon_0)

    Last edited: Jun 6, 2006
  4. Jun 6, 2006 #3
    Thanks a lot, i understand it better now!
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