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Finding the Electric Field as a Result of Two Point Charges

  1. Oct 2, 2014 #1
    1. The problem statement, all variables and given/known data
    There is a −3 µC point charge at (0,0,4) and a +3 µC point charge at (0,0,-4). What is the magnitude and direction of the electric field at point (0,0,8)? What is the magnitude and direction of the electric field at point (0,0,8)?


    2. Relevant equations
    [itex]E = \frac{ k_e q }{ r^2 }[/itex]


    3. The attempt at a solution
    It should be as simple as just adding the electric field caused by each point charge.
    [itex](0,0,8)[/itex]:
    [itex](0,0,8) - (0,0,4) = (0,0,4)[/itex]
    [itex]
    (0,0,8) - (0,0,-4) = (0,0,12)[/itex]
    [itex]\frac{ k_e
    −3 \mu C (0,0,4) }{ 4^3} + \frac{ k_e 3 \mu C (0,0,12) }{ 12^3 }[/itex]

    -1685.625 + 187.29166 = -1498.33334
    However, the answer I should be getting (apparently) is 609

    (4,4,0):
    (4,4,0) - (0,0,4) = (4,4,-4)
    (4,4,0) - (0,0,-4) = (4,4,4)

    ke −3 µC (4,4,-4) / (4^2 + 4^2 + 4^2)^(3/2) + ke 3 µC (4,4,4) / (4^2 + 4^2 + 4^2)^(3/2)

    ke −3 µC (4,4,-4) / (48)^(3/2) + ke 3 µC (4,4,4) / (48)^(3/2)

    (-324.4, -324.4, 324.4) + (324.4,324.4,324.4) = (0,0, 648.8)
    However, the answer I should be getting is 487

    Am I doing something wrong?
    (and why is it ignoring my LaTex tags?)

     
    Last edited: Oct 2, 2014
  2. jcsd
  3. Oct 2, 2014 #2
    Oops, sorry, didn't mean to double post.
     
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