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4 charges, find potential

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

    4 charges, distributed as follows

    12*10[itex]^{-6}[/itex] C @ (-4,4)
    12*10[itex]^{-6}[/itex] C @ (4,4)
    -6*10[itex]^{-6}[/itex] C @ (-4,-4)
    -3*10[itex]^{-6}[/itex] C @ (4,-4)

    Calculate the potential at the origin if the potential at infinity is zero.

    2. Relevant equations

    V= U/q = -W/q = ∫E*dl = k*q/r

    for multiple point charges, find V for each one, and sum them up

    3. The attempt at a solution

    [itex]V1 = V2 = \frac{k*12*10^{-6}}{(4*\sqrt{2}/2)} [/itex]
    [itex]V3 = \frac{k*-6*10^{-6}}{(4*\sqrt{2}/2)} [/itex]
    [itex]V4 = \frac{k*-3*10^{-6}}{(4*\sqrt{2}/2)} [/itex]

    [itex]V1+V2+V3+V4 = \frac{k*3*10^{-6}}{4*\frac{\sqrt{2}}{2}}*(4+4-2-1) = 47676.7

    So, I factor out the k, the 3*10e-6, and the 1/(r) from each Vi, then multiply it by 4+4-2-1 =5

    this answer is not right. Any pointers?

  2. jcsd
  3. Feb 1, 2012 #2


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    Science Advisor
    Homework Helper

    hi jehan60188! :smile:

    shouldn't r be 4√2 ? :redface:
  4. Feb 1, 2012 #3

    4^2 + 4^2 = 32 = 4 Sqrt(2)
    why, WHY did I divide by 2?!

    divided my solution by 2 (since it was sqrt(2)/2 in the divisor), and got the right answer! thanks!

    mods, please feel free to close topic
    Last edited: Feb 1, 2012
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