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Superposition of Electric Fields

  1. Oct 15, 2011 #1
    I know this problem is simple enough but I can't get the hang of it

    Find the electric field at point A in the diagram if (a) q1=2.00 μC and q2=3.00 μC. (b) q1=2.00 μC and q2= -3.00 μC.


    Thank you.

    P.S. If you can explain how you solved the problem that would be great. I'd really like to know what it is that I'm doing.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    (9E9)(2E-6)(3E-6)/(0.5)^2=0.216 but the text tells me the answer is 1.26E5 for (a) so I'm not sure how to go about this.
  2. jcsd
  3. Oct 15, 2011 #2
    You're using Coulomb's law, that is only applicable to finding the force between two charges. You are looking for the field at A. To find the field from a point charge, you would use kQ/r^2, where k is Coulomb's constant, Q is the source charge, and r is the distance from the charge. Electric fields super impose, so you can find the field from each charge separately and then add them together.
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