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Point charge and electric flux

  1. Feb 5, 2011 #1
    1. The problem statement, all variables and given/known data
    You measure an electric field E at a distance x from a point charge. What is the electric flux through a sphere whose center is at that distance and whose radius is less than x from the charge?

    2. Relevant equations
    E*dA = (q_enc)/(e_0)

    3. The attempt at a solution
    I'm not sure that I'm understanding the question....The sphere does not enclose the point charge since its center is at x and its radius is less than x from the charge, so doesn't that mean q_enc = 0 and the flux is 0? (I have the answer so I know it's not zero, but I don't understand what I'm missing conceptually here....)
  2. jcsd
  3. Feb 5, 2011 #2
    net flux is 0
    it means the new electric field lines crossing the total surface is 0
    look at pic ... all field lines entering exit the Gaussian surface !! so net field through surface is 0

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  4. Feb 6, 2011 #3


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    Staff Emeritus
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    Homework Helper

    I believe that is correct.
    That's weird, what is the "correct" answer that you have been given?
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