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Homework Help: AP Physics C question

  1. Aug 16, 2007 #1
    1. The problem statement, all variables and given/known data
    In the interior of a sphere is a charge -q. On the surface of the sphere are two charges, each q, as shown in this figure:
    1982 Physics C.JPG
    2. Relevant equations
    Electric Flux through a Closed Surface=(Charge Enclosed)/Epsilon_0
    3. The attempt at a solution
    This was a question in the 1982 AP Physics C E&M Free Response: problem 1, part c.
    Unfortunately, I cannot find this test anywhere on the internet. I was, however, able to find the solution to the test. The solution given to this question is:
    1982 Physics C Solution.JPG
    If anyone is able to find the AP Physics C test in question, I would greatly appreciate it.
    What I do not understand is that since two charges are on the surface of the sphere, the electric field due to these charges at the points where they are located would be undefined, and thus the electric flux through the surface should also be undefined. According to the creators of the test, however, the charges *on* the sphere are considered to be "enclosed by the sphere."
    I would think that the two charges on the sphere would neither be enclosed by it nor outside of it, therefore the flux would be undefined.
    Any help would be highly appreciated.
    Thank you in advance.
  2. jcsd
  3. Aug 16, 2007 #2


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    Homework Helper

    I agree with you. Are you sure the closed surface that are referring to is the surface of the sphere itself? The question might refer to a surface enclosing the sphere...
  4. Aug 16, 2007 #3
    No, I'm sure the question was to find the electric flux through the sphere.
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