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Homework Help: Finding the magnitude and direction at a point in an electric field with 2 charges

  1. Oct 3, 2012 #1
    1. The problem statement, all variables and given/known data
    "A point charge of 3*10^-6 C is at the origin and another point charge of -4*10^06 C is at point 0.1m away along the x axis.
    What is the magnitude and direction of the electric field at point 0.15m from the origin along the posting y-axis?

    2. Relevant equations
    E= Q/(4PIε°*r^2)

    3. The attempt at a solution
    Electric Field from the first charge to the point on the Y axis:
    E1 = (3*10^-6)/(4PIε°*0.15^2)

    Electric Field from the Second charge to the point on the Y axis:
    E2 = (-4*10^-6)/(4PIε°*0.18^2)

    Magnitude Of Electric Field = E1+E2=88808N/C

    Direction is 158 Degrees from the X(got this from the vectors)

    This is my answer, my physics is really rusty and I have a gut feeling I've gone completely wrong. A checking and assistance would be appreciated.

  2. jcsd
  3. Oct 4, 2012 #2


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    Science Advisor
    Homework Helper

    welcome to pf!

    hi infected! welcome to pf! :smile:

    (have a pi: π and try using the X2 and X2 buttons just above the Reply box :wink:
    (you mean the positive y-axis?)

    your E1 and E2 magnitudes look ok :smile:

    but i think you've added the magnitudes, instead of using vector addition (ie adding the coordinates separately, or using a vector triangle) :wink:
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