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Homework Help: Find electric field a distance from a charged sheet

  1. Apr 3, 2013 #1
    1. The problem statement, all variables and given/known data

    For a sheet of infinitesimal area, find the electric field 9 mm from the surface if the charge density is 5 μC/mm^2.

    2. Relevant equations


    3. The attempt at a solution

    E=(5x10^-6 C/m^2)/(2*8.85x10^-12)

    = 2.8 x10^5N/C

    I know the correct answer is about 5.6x10^11 N/C, but I'm not sure why. Probably units? I'm not sure how to get N/C at the end when I'm given microcoulombs/mm^2 to begin with. Please help! Thank in advance.
  2. jcsd
  3. Apr 3, 2013 #2
    Yes, this is a problem with the units.
    You need to convert σ into SI units, ie C/m2
  4. Apr 3, 2013 #3
    (5C/m^2) / (2*8.85x10^-12C/Vm) = 2.82x10^11 V/m
  5. Apr 3, 2013 #4


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    What on Earth is a sheet of infinitesimal area ?
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