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Homework Help: What is the resultant vector electric field at the point P?

  1. Feb 26, 2015 #1
    1. The problem statement, all variables and given/known data
    There are 3 charges, each denoted q, the first at (0,a), the second at (0,0) and finally one at (b,0). What is the resultant electric field at point P, (b,a)?

    2. Relevant equations
    =q/(4πεo r2) for a point charge

    3. The attempt at a solution
    So I know I need to use the superposition principle and sum the fields caused by the individual charges but I'm not sure whether I need to consider the fact that their fields wont necessarily be in the same direction.

    My attempt gave me
    E= q/(4πεo (1/a2 + 1/b2 + 1/(a2 + b2)) in the direction the same as sqrt(a2 + b2).

    Thanks for any help, I've been debating this with friends.
  2. jcsd
  3. Feb 26, 2015 #2


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    Science Advisor
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    2017 Award

    Hello again,

    You really need to make a drawing. ##\vec E## is a vector, as is ##\vec F = q\vec E##. Fields add up, so you can calculate the forces separately and then add them up. Vector-wise, as is the habit when dealing with forces !

    Oh, and ##\sqrt{a^2+b^2}## has no direction! It's a number, a scalar.

    Oh, and E ##\propto## 1/r2, not 1/ ( 1/r2 )
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