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Calculating Electric Potential at a Point

  1. Oct 31, 2012 #1
    I'm fairly certain I'm doing this problem right.. But my homework assignment program keeps telling me it's incorrect..

    1. The problem statement, all variables and given/known data
    The drawing shows six point charges arranged in a rectangle. The value of q is 6.78 μC, and the distance d is 0.15 m. Find the total electric potential at location P, which is at the center of the rectangle.

    http://imgur.com/YsSCB
    Associated picture

    2. Relevant equations

    Electric Potential = Ʃ(kq/r)


    3. The attempt at a solution

    So basically, since the +5, -5, +3, -3 charges cancel out, i ignore them. I pretty much plug in (2*7q)/r.

    I end up with 5.09*10^6 V.

    I don't know what I'm doing wrong.. Can you please let me know whether or not this is the correct answer based on the numbers I provided, and if not, suggestions as to where I went wrong.

    Thank you,
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 31, 2012 #2

    SammyS

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    What did you use for r?
     
  4. Oct 31, 2012 #3
    Using the Pythagorean (spelling?) theorem, I got 0.1677m (sqrt(0.15^2 + 0.075^2))
     
  5. Nov 1, 2012 #4
    Any insight?
     
  6. Nov 1, 2012 #5

    haruspex

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    Your calculations all look correct to me. But I'm no electrostatics expert, so I might be missing something wrt units. Millions of volts seems like a big answer, but maybe a microC is a big charge.
     
  7. Nov 1, 2012 #6
    Thanks!

    Like I said, I'm fairly certain that the issue is with the question as opposed to my work. I tried googling a similar problem online, I used their numbers with my reasonings and I got the right answer
     
  8. Nov 1, 2012 #7

    SammyS

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    The method looks good, and I got the same answer.
     
  9. Nov 1, 2012 #8
    That's good to hear I guess ahah, thanks for your help guys
     
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