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Homework Help: Finding the distance between 2 charges in electric equilibrium.

  1. Apr 11, 2013 #1
    1. The problem statement, all variables and given/known data
    Charge A and charge B are 2.2m apart.Charge A is 1.0C, and charge B is 2.0c. Charge C, which is 2.0C, is located between them and is in electrostatic equilibrium. How far from charge A is charge C.

    2. Relevant equations
    E = KcQ1Q2/r^2-------Electric force Formula where E = electric force, Kc = 8.99*10^9, r = radius
    E=Kq/r^2--------------Electric field formula where q = charge of particle, E = electric field, K = 8.99 * 10^9
    EQ = F----------------E = electric field, Q = charge of particle, F = force

    3. The attempt at a solution

    Not really sure how to start this one so if anyone would help me it would be great thanks much in advanced!!!
  2. jcsd
  3. Apr 11, 2013 #2


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    Hi Ram012593! :wink:

    If the distance AC is r, then the distance BC is 2.2 - r.

    Show us what you get. :smile:
  4. Apr 14, 2013 #3
    Ok I've tried setting the formulas for the forces equal to each other since its electric equilibrium so the forces must be the same and tried to solve for ra the radius of the first two and im not sure if i did it incorrectly or i made an algebra mistake it could easily be both as I'm not very good at algebra at the moment if anyone would correct me this would be great thanks much:D. Here is a link to a snapshot i took of what i did so far. If i am doing it correctly which is not likely can someone tell me how I could continue. http://postimg.org/image/q4md6ins1/
  5. Apr 14, 2013 #4


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    Hi Ram012593! :smile:
    Yes, your method is fine, but your algebra has let you down :redface:

    your 1/r2 = 2/(2.2 - r)2 is correct :smile:,

    but you left out the 4.4r term when you expanded that square! :confused:

    (btw, why use two letters, ra, or maybe ra, when one letter will do? :wink:)
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