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Homework Help: Finding the electric field at point P between two charges

  1. Sep 5, 2015 #1
    1. The problem statement, all variables and given/known data
    Find the electric field (both magnitude and direction) at point P located between the charges q1 = -3C and q2 = +4C. Point P is 1/3 of the charges' separation distance from q1 and 2/3 of the charges' separation distance from q2.

    2. Relevant equations
    E = kq/d^2
    Etotal = E1 + E2

    3. The attempt at a solution
    I am able to infer that the direction of the electric field points to the left of P. I also know that, due to the above equations, Etotal = (9E9 * 3)/(2/3x)^2 + (9E9 * 4)/(2/3x)^2 therefore Etotal = 3.24E11/x^2

    However, I am having trouble finding the distance between the charges q1 and q2. Is there a point between q1 and q2 where the electric field is zero that I can set kq1/d^2 equal to kq2/d^2? I would appreciate any help finding the distance between the two given point charges.
    Last edited: Sep 5, 2015
  2. jcsd
  3. Sep 5, 2015 #2


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    Homework Helper

    The charge separation must be given, possibility is that you missed this information somehow or else the answer is to be expressed as a function of charges distance.
  4. Sep 5, 2015 #3
    If it isn't given, I would assume that it is 1 meter.
  5. Sep 7, 2015 #4
    Thank you for the help. I emailed my professor, and he confirmed that the answer will be expressed as a function of the charges' separation distance.
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