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Homework Help: Find electric Field through 3 plates using Gausses Law

  1. Feb 13, 2013 #1
    1. The problem statement, all variables and given/known data
    The figure shows three very thin parallel planes of charge with equal separation 8 cm between them. The charge density of the middle plane is +4 nC/m2 (nC = "nano Coulomb") and that of the two outer planes is -2nC/m2. Use Gauss's law to solve the following questions. We choose positive electric field along the y-direction.
    What is the Electric Field at point C?

    2. Relevant equations
    E=ρD/ε Electric Field at position D

    3. The attempt at a solution
    I've tried to Calculate the E at distance between The top Positive ρ and the point C and from the bottom ρ to point C. Should these two be equal?
    From top:
    (4e-9c/m^2 * 0.004m) / ε to give me field to point C

    From bottom:
    (2e-9c/m^2 * 0.004m) / ε to give field to point C

    I know the field results in a - I've tried to add them to get the answer and subtract.
    What am I to do from this point?
    Am I using the wrong equation?


    Attached Files:

  2. jcsd
  3. Feb 13, 2013 #2


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    Homework Helper
    Gold Member
    2017 Award

    The question asks you to use Gauss' law to find the answer. Since you want the field at point C, you should try to construct a Gaussian surface that goes through C. Choose the shape of the Gaussian surface so that you can take advantage of any symmetry in the problem.
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