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Homework Help: Electric Field and Magnitude Problem

  1. Sep 3, 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
    Not sure which of these rules would apply. Also I suck at vectors
    F = k x q1 x q2 / r^2

    E = k x Q / r^2

    3. The attempt at a solution

    Electric Field Magnitude.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.
    Last edited: Sep 3, 2014
  2. jcsd
  3. Sep 3, 2014 #2


    User Avatar
    Gold Member

    Step 1:
    Decompose the E field you got at point P due to q1 to horizontal and vertical components.
    Do the same for E field you got at point P due to q2.
  4. Sep 3, 2014 #3

    Doc Al

    User Avatar

    Staff: Mentor

    That's exactly correct.

    Keep going! Find the field from each charge, then find the resultant field by adding the vectors.
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