1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Finite Line Charge's Electric Field?

  1. Jan 31, 2009 #1
    [​IMG]

    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 r to the right of the end of Q.

    1. The problem statement, all variables and given/known data
    Calculate the x-component of the electric field produced by the charge distribution Q at points on the positive x-axis where x>a (i.e., r>0) in terms of some or all of the variables k, q, Q, a, and r, where k=\\frac{1}{4\\pi\\epsilon_0}.


    3. The attempt at a solution
    I'm having a problem visualizing the distance between the charge and the point. I understand that e=KQ/R^2. However, I have no idea how to get R.
    I would do: (k*dQ)/(r+a-x)...
    (kQ/a) [integral]1/(r+a-x)dx


    But I don't think that looks right. Can anyone give me a few pointers?
     
    Last edited: Jan 31, 2009
  2. jcsd
  3. Jan 31, 2009 #2

    Delphi51

    User Avatar
    Homework Helper

    Looks great! Except you forgot to square the distance (r+a-x) in the integral.
    Also, something must be done about dq to express it in terms of dx so it will be possible to integrate. The charge on a segment dx would be dq = (q/a)dx because the charge per unit length is q/a.
    Finally, the integral is awkward with the r and a in there. You can get it with math techniques of course (let R= r+a-x), but it might be better to think of the distance as R and integrate it from R = a+r to r. Of course dR = dx.
     
  4. Jan 31, 2009 #3
    Thank you for your help. I needed someone to confirm the distance for me since I was completely lost on that part.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?