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Homework Help: Net Electric Field of 2 charged particles fixed to X-axis

  1. Sep 22, 2010 #1
    2 Particles are fixed to an x-axis:
    q1=2.1*10^-8 C @ x=.2m
    q2=-4.00q1 @ x=.7m

    We are trying to find the coordinate on the x-axis where the net electric field produced by the particles = 0.
    The equation I have is


    I got what i thought was q2 first, by multiplying 2.1*10^-8 by -4.00 to get -8.4*10^-8. From there I equated E1 & E2:
    ((8.99*10^9)(2.1*10^-8))/r^2 = ((8.99*10^9)(-8.4*10^-8))/r^2
    from there, I had no idea how to solve for r.
    I simplified the constant 8.99*10^9 with the respective q's, but just couldn't figure out how to solve for r without it canceling into 1 and having two numbers equaling each other. :confused:
    Please help, I have a number of problems like this to do for this chapter.
  2. jcsd
  3. Sep 22, 2010 #2
    Almost correct except [tex]r[/tex] in your equation
    [tex]r[/tex] is a distance from the charge you are considering. So each [tex]r[/tex] on the left side and right side of your equation should not be equal. One should be include the distance between two point charges.
  4. Sep 23, 2010 #3
    Wait, so one of the r's should be .5m, the distance between the two particles?
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