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Homework Help: Finding the electric field magnitude, and angle below the horizontal

  1. May 8, 2009 #1
    1. The problem statement, all variables and given/known data
    In the figure below d = 2.6 cm. What is the electric field at the position indicated by the dot in the figure?

    2. Relevant equations

    E = charge/4*pi*epsilon_0*distance^2
    The figure is on the attachment.
    3. The attempt at a solution
    I decided to first find only the magnitude from each of the fields on the point.
    charge 1 = 10 nC;
    charge 2 = 5 nC;
    charge 3 = -5nC
    *I put all of the charges into Coulomb before any calculations
    E1 = Kc1/5d^2;
    E2 = Kc2/d^2;
    E3 = kc3/4d^2;
    After adding all of the Es together I get the wrong answer (as far as magnitude).
    Answer is: 7.9 × 104 N/C, at 5.2° below the horizontal

    Attached Files:

  2. jcsd
  3. May 9, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You can't just add up the magnitudes like ordinary numbers (if that's what you did). You must add them as vectors. What is the direction of each field?
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