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What is the electric field at this point?

  1. Feb 21, 2017 #1
    1. The problem statement, all variables and given/known data

    A charge -3.2 micro-coulombs is spread evenly throughout a rod of length (a). At a distance (b) from the rod, what is the electric field?

    a = 1.2 m
    b = 3.4 m

    So basically, you start at zero and then there's a line of charge horizontally to the right from 0 to 1.2 meters, and then at 3.4 meters to the right of the origin there is a point that is distance b away from the end of (a), and I need to find the electric field there.

    2. Relevant equations

    E = kq/r^2

    charge density = dq/dx

    3. The attempt at a solution

    I used E = kq/r^2

    I knew that the charge density = dq/dx

    So I set up the integration like this: E = integral(k/r^2)dq

    Then I switched to terms of dx... E = integral((k * charge density)/r^2)dx

    Then I plugged in 3.4 + x for r... E = integral((k * charge density)/(3.4 + x)^2)dx

    k and the charge density were constants for I pulled the out of the integral and integrated 1/(3.4+x)^2dx from 0 to 1.2. I did used u substitution to do this.

    I was wondering if I used the correct method here, and if my answer was correct.

    I got -1840 N/C
  2. jcsd
  3. Feb 21, 2017 #2


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    Science Advisor
    Homework Helper
    2017 Award

    Hi Luke,
    I think you're doing just fine. Why the hesitation ?
  4. Feb 21, 2017 #3


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    Staff: Mentor

    This is rather vague. You need to specify the geometry more precisely. From where on the rod is (b) measured and in what direction?
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