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Homework Help: Electric Field

  1. Jan 26, 2017 #1
    1. The problem statement, all variables and given/known data
    electri field.PNG

    2. Relevant equations

    Ex=1/k*1/(a^2/2)*1/(sqrt2)*cos(theta)*(sum of charges)
    Ey=1/k*1/(a^2/2)*1/(sqrt2)*sin(theta)*(sum of charges)
    3. The attempt at a solution
    So first off I can see that I don't need to calculate the force in the x direction as each q cancels out when arranged appropriately
    For Ey I get:
    =1.523E-16 N/C

    Use Pythagorean theorem but that is unnecessary do to an absence of an x component
  2. jcsd
  3. Jan 26, 2017 #2
    just go "by parts" try finding y comp of charge 1 and 4 then 2 and 3 and just add them up. or realize that charges 1 and 2 resultant y component is the same as 3 and 4 so you just have to do one calculation and multiply by 2
  4. Jan 30, 2017 #3
    I did as you said using parts and still came up with the same answer of 1.523E-16 N/C.
  5. Jan 30, 2017 #4
    that doesnt seem right... what are you using to calculate the field? E=F/qtest this q is normally a test charge (1C) and F = kQ*qtest/r2 so the test charge cancels out which makes sense since you want the field created by the source charge.
    so Fx=Fcos(theta)
    ps: r is the distance between the charge and the point where you are evaluating the field
    ps2: yeah it doesnt seem to be a unit problem, i dont know where you got the 1/k or the sqrt2

    maybe those will help clearing things up
    Last edited: Jan 30, 2017
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