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Homework Help: Determining the electric potential at a distance

  1. Sep 27, 2012 #1
    1. The problem statement, all variables and given/known data

    The electric potential of a very large isolated flat metal plate is 2000 V. The plate carries a uniform distribution of charge with surface density σ=1 μC/m2. Determine potential V at a distance x=1 cm from the plate. Assume that point x is far from the edges and that x is much smaller than the size of the plate.

    2. Relevant equations

    To find the magnitude of the electric field I know I have to use: |E|=σ/2ϵ0

    3. The attempt at a solution

    I'll be honest I have no clue how to solve this problem, any pointers in the right direction would greatly help!
  2. jcsd
  3. Sep 29, 2012 #2


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    Well, you've got E, and they are asking for potential, so what equation do you know which connects E and V ?
  4. Sep 29, 2012 #3
    Would I be wrong in stating that since it's a very large plate with uniform charge density, it isn't a point charge. The formula that I have that links those two informations are:

    ΔV = -∫Eds, and since the electric field is constant,

    ΔV = -Es

    ΔV = -σ/2ϵ0 times s

    ΔV = -((1 μC/m2)/(2ε0)) times 0.01m

    It seems like it's too simple solving like that, I feel like I'm missing something
    Last edited: Sep 29, 2012
  5. Sep 29, 2012 #4


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    That is the right answer. The question was more simple than you thought. The final step is to use the initial V and change in V to get the V 1cm away.
  6. Sep 29, 2012 #5
    I'm not sure I understand what you mean by that last reply

    If I read it right: The answer gives me ΔV, and I have VA, I want VB, right?

    So I should do: ΔV = VB - VA ==> ΔV (That I found) = VB - 2000V

    So ΔV + 2000V = VB (the volt at 1cm away)?
  7. Sep 29, 2012 #6


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    yes, that's right.
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