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Homework Help: Calculating electric field due to charge distribution

  1. Apr 4, 2015 #1
    1. The problem statement, all variables and given/known data
    http://imgur.com/EiCFIDe [Broken]

    2. Relevant equations
    E = kq/r2
    λ = dq/dx
    Q = λa

    3. The attempt at a solution
    Here is the book solution:
    http://imgur.com/aKSeKo0 [Broken]

    I need help with part (a). I understand everything in the solution except for the distance they used for between (r2 in the equation above). It seems they used (a+r-x) and they say that is the distance between a segment at x and the charge q. What does q have to do with the problem at all? Part (a) asks for the electric field due to the charge distribution Q where x > a. So shouldn't the distance be between dx(a segment on the charge distribution) and x?
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Apr 4, 2015 #2


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    Homework Helper
    Gold Member
    2017 Award

    You are right, it should not have mentioned q in the solution for (a). But the derivation is OK if you think of r as the distance from the right end of the rod to some arbitrary point P located to the right of the rod.
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