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Homework Help: Finding electric field via potential

  1. Oct 3, 2011 #1
    1. The problem statement, all variables and given/known data

    The plastic rod of the length L=1 m has a non-uniform charge density λ=cx
    where positive constant c =2x10^-6 [some unit]. What unit c has to have? Find the electric
    potential at the point on the x axis 1 m to the left from the left end of the rod. Find the
    electric field at that point via potential. What is the direction of the field

    2. Relevant equations

    V = k integral(0 to L) dq/r

    E = -dV/dx

    3. The attempt at a solution

    Found everything except electric field. I've tried and gotten so confused as to how to implement it. I got this so far:

    dV = kλdx/(d+x)

    dV/dx = kλ/(d+x)

    E = -k(c)(1m)/(2m) = -8.99 x 10^3 N/C

    I know it's wrong but I'm so lost as to where to fix it. Thanks
  2. jcsd
  3. Oct 4, 2011 #2
    I would like to know if either:

    -3.47 x 10^3 N/C


    -1.45 x 10^4 N/C

    Are correct. Thank you :)
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