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Homework Help: Electric field charge problem

  1. Jul 11, 2008 #1
    1. The problem statement, all variables and given/known data

    The electric field strength 5cm from a very wide charged electrode is 1000N/C. What is the charge (in nC) on a 1cm diameter circular segment of the electrode?

    2. Relevant equations



    3. The attempt at a solution[/b

    I tried to figure out n, so that I can plug it into n=Q/A to figure out Q. But it didn't work.
  2. jcsd
  3. Jul 11, 2008 #2
    Since the electrode is so wide compared to how far away the electric field is measured at, we may treat the electrode as an infinite insulating plane of charge for which the electric field is given by Gauss's Law. It yields [tex]E\equiv\frac{\sigma}{\epsilon_0}[/tex] where [tex]\sigma[/tex] is the area charge density of the plate. This is essentially what you had. You're given the electric field. Just make sure that when you calculate the area that you use the radius since you are given the diameter.
  4. Jul 11, 2008 #3
    What equation do I need to use to apply the area and the electric field to get the charge? n=Q/A?
  5. Jul 11, 2008 #4
    I'm not sure what your n is supposed to be.. Apparently is the area charge density which is conventionally denoted as [tex]\sigma[/tex]. You are given the electric field so you can find the sigma and you also know the area so you can find the charge.
  6. Jul 12, 2008 #5


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    Two symbols are being used for charge density here:

    n = Q/A

    [tex]\sigma[/tex] = Q/A
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