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Homework Help: Potential Difference Near a Charged Rod

  1. Feb 9, 2009 #1
    1. The problem statement, all variables and given/known data

    A long rod of length L = 7.8 m carries a uniform charge Q = -6.5e-08 coulombs.
    Calculate the potential difference VC - VA. The distance c is 4 cm, the distance b is 11 cm, and the distance a is 4 cm. Only part of the rod is shown in the diagram (it is longer than shown).

    2. Relevant equations

    Erod = (9e9)*[tex]\frac{2Q/L}{r}[/tex]
    [tex]\Delta[/tex]V = - [tex]\int[/tex] E dl

    3. The attempt at a solution

    I figured that since A is the same distance horizontally as B from the rod, there would be no change in potential since its not acting in that direction. So I was just going to find Vc-Vb

    I set up my integral as follows:

    V = - (9e9)*[tex]\frac{2Q}{L}[/tex][tex]\int[/tex] [tex]\frac{dr}{r}[/tex]
    Integral going from upper to lower: B to C

    I just don't think I'm headed in the right direction. It seems like the answer is not going to be what I want it to be.
    Last edited: Feb 9, 2009
  2. jcsd
  3. Feb 9, 2009 #2


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    Homework Helper

    That's right.
    That looks ok too.
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