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Homework Help: Electric field point charges

  1. Sep 4, 2013 #1
    1. The problem statement, all variables and given/known data

    Two points are resting on a string. The first point is resting at x = 6.0 m and has charge q1 =−7.1 µC. The second point is resting at x = −4.0 m and has charge q2 = −4.3 µC.
    At what location is the total electric field zero from the two points(other than infinity)?

    2. Relevant equations

    [tex]E =\frac{KQ}{r^2}[/tex]

    [tex]\frac{q_1}{r_1^2} = \frac{q_2}{r_2^2}[/tex]

    3. The attempt at a solution

    I divided away the constant K from my second equation because they cancel out when you set them equal to each other.

    I don't know what my [tex]r_1,r_2[/tex] should be here?
  2. jcsd
  3. Sep 5, 2013 #2
    Why don't you set the distance from the first charge x and define the distance from the other with x and the distance between the two charges? Thus you introduce only one variable in one equation.
  4. Sep 5, 2013 #3
    Don't forget that the contribution to the electric field from each charge has direction, so, if the point is between the two charges, the contribution from the charge at x = 6 is pointing in the negative x-direction, and the contribution from the charge at x = -4 is pointing in the positive x-direction.
  5. Sep 6, 2013 #4
    I am not following can you guys elaborate more please?
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