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Homework Help: Electric Potential-finding unknown charge

  1. Feb 16, 2010 #1
    1. The problem statement, all variables and given/known data

    The potential equals 7.52 V at the midpoint between two point charges that are 0.91 m apart. One of the charges is 1.11 x 10-9 C. Find the value of the other charge.

    2. Relevant equations

    V = k [sum] (q/r)

    3. The attempt at a solution

    7.52=k[(1.11 x 10-9 / 0.455m ) + ( x / 0.455m )]

    This gives me -7.3x10^-10, which is incorrect, but I cannot think of any other way to approach this problem.
     
  2. jcsd
  3. Feb 16, 2010 #2

    kuruman

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    Your approach is correct and the numbers match the approach. How do you know it is incorrect? Do you know the correct answer?
     
  4. Feb 16, 2010 #3
    I am entering the answers in Webassign and it marked my answer as incorrect. I think there must be a mistake because no one I've showed it to has gotten a different answer.
     
  5. Feb 16, 2010 #4

    kuruman

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    It is time to ask your teacher. You might do everybody a favor.
     
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