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Uniform line of charge and point charge

  1. Sep 8, 2013 #1
    1. The problem statement, all variables and given/known data
    An infinite line charge of uniform linear charge density lambda = -3.1 mu or micro CC/m lies parallel to the y axis at x = -1 m. A point charge of 0.7 mu or micro CC is located at x = 2.5 m, y = 3.5 m. Find the x- and y-components of the electric field at x = 3.5 m, y = 3.0 m.

    2. Relevant equations
    flux = E*A = Q/ε
    E = kQ/r^2

    3. The attempt at a solution
    X axis:
    To find the electric field from the line only: gaussian cylinder, centered on the line and r = 4.5m.
    E*2∏*4.5*L = λL/ε -> E1 = λ/(ε*9*∏) to the left

    From the point:
    E2 = K(.7*10^-6)/1.25*sin(63.43°) to the right

    Ex = E2-E1 Right?

    Y axis:
    The line don't matter because it cancels itself out. right?
    Ey = K(.7*10^-6)/1.25*cos(63.43°) Down

    Both answers need to be in kN/C, I'm at a loss, do you guys have any ideas? I have tried many different answers and I've checked all of the units.
    Last edited: Sep 8, 2013
  2. jcsd
  3. Sep 8, 2013 #2


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    Your work looks good to me. What did you get for your final answer?
  4. Sep 8, 2013 #3


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    What are your numerical results?

  5. Sep 9, 2013 #4
  6. Sep 9, 2013 #5


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    Does WolframAlpha assume the argument of trig functions is in degrees or radians?
  7. Sep 9, 2013 #6
    Welp, I just found my mistake. Damn Radians!
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