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Electrostatic problem

  1. Sep 30, 2010 #1
    1. The problem statement, all variables and given/known data

    I'm looking at Y.K.Lim's Problems and solutions in Electromagnetism and there's one thing that's confusing me:

    [PLAIN]http://img545.imageshack.us/img545/2218/capturegb.png [Broken]

    2. Relevant equations

    Where does the square in r comes from? When in the beginning it says that the electric field is:

    [tex]E=A\frac{e^{-br}}{r}e_r[/tex] not[tex]E=A\frac{e^{-br}}{r^2}e_r[/tex]

    What am I missing?

    And what should [tex]e_r[/tex] stand for? Charge?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 30, 2010 #2
    This E-field is not due to a single charge. It is due to a distribution of charges, so it needs not be proportional to r^2. For example, a uniformly charged plane produces uniform E-field on each side of the plane, obviously not proportional to distance^2, correct? :smile:
    [tex]e_r[/tex] is the unit radius vector.
  4. Sep 30, 2010 #3
    Ok it needs not be proportional to r^2, but why did he put it then? When taking the divergence of the field?
  5. Sep 30, 2010 #4
    Oh I see. Then it seems to me that it's a typo :wink:
  6. Sep 30, 2010 #5
    Oh, I thought it's something new I didn't know XD
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