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Homework Help: Electric monopole, dipole of sphere

  1. Feb 28, 2008 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    3. The attempt at a solution

    I am not sure what to do with the -4q.(did something with this)
    I was thinking of ignoring it, and treating it like if it is really far away, however since it is only twice the distance from the origin as the two +q charges, i am not sure what to do with it.

    ** Edit
    is there a way to add all three charges and calculate how they are felt in the origin?

    SORRY for posting this twice I was trying to edit,because i added my drawing, and now i dont know how delete the other thread!
    Last edited: Feb 28, 2008
  2. jcsd
  3. Mar 7, 2008 #2

    Shooting Star

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    Homework Helper

    Your diagram doesn't seem to be correct. The charge -4q is distributed over a sphere of radius R, so it covers the other two charges. Also, you cannot ignore given charges at your will. :smile:

    Do you know what is meant by the monopole moment?

    Write down the expressions for dipole moments for discrete and continuous charges. You must be knowing the formulae. Then you just have to add the two. If you note the spherical symmetry of the -4q charge distribution, the dipole moment becomes very easy to find.
    Last edited: Mar 7, 2008
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