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Homework Help: Griffiths Example 3.8

  1. Feb 17, 2008 #1
    [SOLVED] Griffiths Example 3.8

    1. The problem statement, all variables and given/known data
    Please stop reading unless you have Griffiths E and M book.

    In Example 3.8, Griffiths makes two claims without justification that I want justification for. First, he says that V=0 in the equatorial plane (I assume this means that x-y plane). Second, he says that [tex]V \to -E_0 r \cos{\theta}[/tex] for [tex]r >>R[/tex]. Where does the cosine come from?

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 17, 2008 #2
    The problem is originally defined in cartesian coordinates. Now that we are using the Legendre Polynomials it has to be in spherical coordinates.

    Orginally:
    [tex]V \to -E_0 z[/tex]
    goes to
    [tex]V \to -E_0 r \cos{\theta}[/tex]
    since
    [tex]z = r \cos{\theta}[/tex]
     
  4. Feb 17, 2008 #3
    And how do you know V=0 all over th equatorial plane?
     
  5. Feb 17, 2008 #4
    It is an uncharged metal sphere, so we basically assume it was grounded beforehand
     
  6. Feb 17, 2008 #5
    I see. Thanks.
     
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