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Homework Help: Electric field from uniform charge of finite length

  1. Dec 7, 2012 #1
    1. The problem statement, all variables and given/known data
    A uniform charge Q of length L is placed on the x-axis with one end at the origin as shown


    a) Find the contribution dE (vector) to the electric field at P on the y axis a distance y from the origin, from the charge at x in dx, in terms of Q, L, dx, ke, x and y

    b) Find the total E (vector, in component form) from the whole line of charge at y on the y-axis in terms of Q, L, ke, y; also find E (vector) for |y| >> L

    c) Use the result in (b) to obtain the behavior of E (vector, in component form) on the y-axis if L is infinite in the +x direction (left end remains at 0)

    2. Relevant equations
    elin.gif I believe this is all I need?

    3. The attempt at a solution

    [itex]\huge dE = \frac{k\lambda dx}{r^2}<\frac{x}{r},\frac{y}{r}> = \frac{kQdx}{(x^2 + y^2)^{\frac{3}{2}}L}<x, y>[/itex]

    This doesn't look right to me, and I'm a bit stuck on trying to integrate this... I'd assume you integrate with respect to X from 0 to L...
  2. jcsd
  3. Dec 7, 2012 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Well let's check it then: what was the reasoning you used to get to that equation?
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