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Homework Help: Linear charge

  1. Sep 17, 2012 #1
    1. The problem statement, all variables and given/known data[/b]

    Positive charge Q is distributed uniformly along the x-axis from x=0 to x=a. A positive point

    charge q is located on the positive x-axis at x=a+r , a distance to the right of the end of Q.

    Observe the figure below

    My goal is to try to explain the problem to make sure I understand it since a similar one will be on my exam, and also get some questions that I don't understand addressed. (:

    1. Calculate the x-component of the electric field produced by the charge distribution Q at points on the positive x-axis where x>a.

    [itex]\lambda[/itex]= [itex]\stackrel{Q}{a}[/itex]

    dQ=[itex]\-lambda[/itex] dx (I dont know why lambda is negative)


    First things First I know that the distance of Q is a and the distance from Q to a test point q+ is = a+r which the problem statement sets to x for simplicity.

    -[itex]\aintx[/itex] [itex]\stackrel{Q}{a}[/itex]dx

    Here is where I get confused I dont understand why the insert [itex]\stackrel{k}{x^2}[/itex]
    not including the point charge q?

    after that it is just simple integrals and algebra.

    Ultimately getting an answer of [itex]\stackrel{Qk}{a}[/itex]([itex]\stackrel{1}{a}[/itex]-[itex]\stackrel{1}{a+r}[/itex])

    2. Calculate the magnitude of the force that the charge distribution that Q exerts on q.

    Here i'm also confused isn't the answer just a simplified version of part 1?


    Thanks for the help!
  2. jcsd
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