1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Asymptotic behavior quadrupole potential

  1. Apr 14, 2010 #1
    1. The problem statement, all variables and given/known data

    Find the asymptotic behavior of a quadrupole consisting of a -2 charge at the origin and +1 charges at z = +/- 1.

    2. Relevant equations


    3. The attempt at a solution

    You can construct the Coulomb potentials for these three charges and show that for large r, they all go as 1/r. The problem is that if you add them together, for large r, the -2 cancels the 2*1, so for large r you actually get 0/r. This makes the potential go to zero more quickly than 1/r, and 1/r doesn't seem like a fitting description of the asymptotic behavior. How do I go about incorporating this?
  2. jcsd
  3. Apr 14, 2010 #2


    User Avatar
    Homework Helper
    Gold Member

    Taylor expand your expression for the total potential about the point 1/r=0
  4. Apr 14, 2010 #3
    Yup, that worked. Thanks.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook