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Electric Fields help

  1. Feb 11, 2010 #1
    1. The problem statement, all variables and given/known data

    The electric field midway between two equal but opposite point charges is 894 N/C, and the distance between the charges is 17.2 cm. What is the magnitude of the charge on each?

    2. Relevant equations

    E = Fe/q

    Fe = kq1q2/r^2

    3. The attempt at a solution

    Electric field = k*q/r^2 = 447 N/C. You know r and k, so just solve for q.

    I tried about 5 times already and it is always wrong my most recent attempt I divided the Electric Field by two so I had 446 N/C = 8.99e9 * q/.172^2. But it was wrong.

    I might have typed this up wrong but I am new here, sorry. If you guys could help me that'd be great. Thank you.
    Last edited: Feb 11, 2010
  2. jcsd
  3. Feb 11, 2010 #2


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    Homework Helper

    Hi matt, welcome to PF.
    You are finding the field at the midpoint of the two charges. Then what is r?
  4. Feb 12, 2010 #3
    0.086 m?

    Then how would I set that up? Is the Electric Field also divided by 2?
  5. Feb 12, 2010 #4
    No. The electric field has it's formula as a function of the distance of each charge.

    Do you know how to write the expression for the electric field at some point on the line connecting the charges? (name the distance from one charge x)
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