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Homework Help: Components of an electric field / charges

  1. Jun 3, 2008 #1
    1. The problem statement, all variables and given/known data
    four point charges are arranged at the corners of a square, as shown. a = 0.1m, q = 10^-3 coulombs

    (+6q)* *(-3q)<-----------3a------------->P

    an * indicates a point charge
    the distance between each vertice is equal to 'a = 0.1m'
    the y axis is vertical, the x axis is oriented horizontal

    a) what is the y component of the electric field E at point P?

    b) which charge, the +6q or the -3q gives the larger contribution to E at point P?

    c) what is the force on a -12microcoulomb charge placed at point P?

    2. Relevant equations

    not sure with this one -- do i use pythagorean theorem?

    E = kq/r^2 where E is electric field, k is constant 9*10^9, q is the charge, r is the distance

    3. The attempt at a solution

    for a) i think i find the net electric field of all four point charges using E = E1 + E2 + E3 + E4, but am not sure how to derive the y component, do i use the pythag theorem, do i use a/2 as the height, and (3a + a/2) for the base

    i am confused now with how to use that to find the y component

    any help with working throught this problem is greatly appreciated, asap please...
  2. jcsd
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