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Electric field strength from two charges

  1. Sep 8, 2014 #1
    1. The problem statement, all variables and given/known data
    Two identical point charges, q1 = +2.5 x 10-6 C and q2 = +2.5 x 10-6 C, are placed as shown in the diagram below. Point P is a distance 0.05 m from q1 and 0.12 m from q2, such that the angle at P is 90 degrees. Calculate the magnitude of the Electric field E at point P.

    2. Relevant equations

    E = k x Q / r^2

    This plus vector which I suck at.

    3. The attempt at a solution
    Electric Field Magnitude zz.jpg

    So I have created the diagram and I believe I have to use the second formula twice, along with some trigonometry, but I'm not sure.

    E1 = k x Q1 / r^2
    E1 = k x +2.5 x 10^-6 / 0.05^2
    E1 = 9 x 10^6

    E2 = k x Q2 / r^2
    E2 = k x +2.5 x 10^-6 / 0.12^2
    E2 = 1.563 x 10^6

    I Can't do vectors at all. Please help.
  2. jcsd
  3. Sep 8, 2014 #2


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    So now you have two forces, one along the line q1-P and one along the line q2-P. So happens you know the angle between the two. Google vector addition (images) to get an impression of that magic art. Realize that it's really easy when the vectors are at right angles wrt one another. Something Pythagoreran. Bingo.
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