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Homework Help: Voltage not zero at infinity

  1. Feb 3, 2012 #1
    1. The problem statement, all variables and given/known data

    A point charge q = -8 µC is surrounded by two thick, conducting spherical shells of inner and outer radii a1 = 0.2 m, a2 = 0.3 m, a3 = 0.8 m, and a4 = 0.9 m respectively. The inner shell is uncharged; the outer shell has a net charge Q = -8 µC. At this point in the problem, the potential at infinity is unspecified. Do not assume it is zero.

    If now you are given V(inf) = 1 x 105 V, find the potential at r = 0.1 m.

    2. Relevant equations

    V = ∫E*dr

    3. The attempt at a solution

    voltage from .1 m to .9m = -359672 + -149863 = -509535
    (known from previous steps)

    I have no idea how to get the voltage from .9m to infinity!
  2. jcsd
  3. Feb 4, 2012 #2


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    Homework Helper

    hi jehan60188! :smile:

    the voltage difference from .9m to infinity is the same as it would be if the voltage at infinity was 0 :wink:
  4. Feb 5, 2012 #3
    kk, since the voltage between point A (.9 m) and B (infinity) needs to be 10^5 higher than if it were supposed to be zero, I integrate from .9 to infinity, and then add 10^5
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