Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electric fields of dipole

  1. Sep 8, 2008 #1
    1. The problem statement, all variables and given/known data

    A rod of length 2L lies on the x axis, centered at the origen, and carries a line charge

    density given by t=T(x/L), where T is a constant. (a) Find an expression for the electric

    field strength at points on the x axis, for x>L (b) Show that for x>>L, your result has the

    1/x^3 dependence of a dipole field, and by comparison, determine the dipole moment of the


    2. Relevant equations

    dE = (k dq)/r^2

    3. The attempt at a solution

    dq=Tda, dE= (k dq)/(x-a)^2 = (kT/L) * (a da) / (x-a)^2

    integral dE form -L to +L

    E = (kT/L) * ( - x/(x+L) + x/(x-L) + ln( (x-L)/(x+L)) )

    when x>>L , by using binomial expanding, the result what I have

    1/x^2 dependence. Help !!!!!!!!
    Last edited: Sep 8, 2008
  2. jcsd
  3. Sep 8, 2008 #2


    User Avatar
    Homework Helper

    Could I get confirmation on this question? Normally when electric dipoles are talked of, we would look to find fields for distances perpendicular to the dipole rather than parallel.
  4. Sep 8, 2008 #3
    The situation fof that problem, To find the fields for distances parallel to the dipole.

    I think it doesn't matter whether perpendicular or parallel.

    The result of both situation has 1/^3 dependence of a dipole field, I think

    If you know the answer about perpendicular case, I really appreciate your sincerity

    although that is not exact answer about this problem. Thank you for your reply.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook