1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Griffiths page 150

  1. Feb 24, 2008 #1
    [SOLVED] Griffiths page 150

    1. The problem statement, all variables and given/known data
    Please stop reading unless you have Griffith's E and M book.

    On this page, Griffith's start talking about "pure" and "physical" dipoles. Can someone define what these terms mean?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 24, 2008 #2


    User Avatar
    Homework Helper
    Gold Member

    Isn't it explained pretty clearly in the same page?

    Where exactly are you having difficulty?
    Last edited: Feb 24, 2008
  4. Feb 24, 2008 #3

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    A physical dipole comprises a pair of equal but opposite charges [itex]q[/itex] separated by a vector [itex]2a\hat r[/itex]. The dipole moment is [itex]2aq\hat r[/itex]. By decreasing the separation distance but increasing the charge you can keep the dipole moment constant. A pure dipole has a zero separation distance but a non-zero dipole moment. Such a thing is not physically realizable.
  5. Feb 25, 2008 #4


    User Avatar

    What G means in Ex. 3.8 is that the point charges example is one physical configuration that has a dominant dipole moment. He seems to define a "pure" dipole as a configuration that has ONLY a dipole moment, and no higher moments. As he says, that point charges model is only a "pure" dipole in the limit -->0. The sphere with with cos charge distribution is a pure dipole because its potential for r>R is pure dipole.
    None of this is too clear in G because he does not discuss higher dipole moments in good detail. Some things are clearer in more advanced texts.
  6. Mar 18, 2008 #5
  7. Mar 18, 2008 #6
    DH and pam explained nce...

    You may try to get a copy of Corson and Lorrain for more rigorous treatment of higher terms.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Griffiths page Date
Griffith's QM, Harmonic Oscillator approximate solution eq Mar 6, 2018
Griffiths page 182 Mar 17, 2008
Griffiths page 176 Mar 16, 2008
Griffiths page 80 Feb 11, 2008
Griffiths page 124 Feb 11, 2008