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Uniform Linear Charge

  1. Sep 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A nonconducting rod of length L = 8.15cm has charge -q = -4.23 fC uniformly distributed along its length. What are the magnitude and direction [relative to the positive direction of the x axis] of the electric field produced at point P, a distance a = 12.0cm from the rod?

    NOTE: In the illustration, the rod and P are along the x axis, and P is to the right of the rod (assumed to be the positive end).

    2. Relevant equations
    dE = dq/(4*pi*E0*r2)
    dq = Lambda*dx
    E0 = permeativity of free space = 8.85x10-12
    Lambda = linear charge density = q/L

    3. The attempt at a solution
    I am not sure how 'L' and 'a' are to replace 'r' in the equation above. I have tried r = L + a, but it seems this method does not correctly describe the situation. I then tried to integrate the equation along the limits from 0 to L, but am not sure how to include the additional distance of 'a' into the equation. This seems like a fairly simple question, but my text does not extensively pursue this topic.
  2. jcsd
  3. Sep 28, 2009 #2
    what you have to compute is [tex] \int_0^L \frac {dq} { 4 \pi \epsilon_0 r^2} [/tex]

    where r = the distance from the charge element dq to the point P
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