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Homework Help: Electrostatic potential of circular ring

  1. Apr 7, 2014 #1
    I'm a little stumped with this problem, I have posted a photograph below as there is a diagram to compliment the question

    ImageUploadedByPhysics Forums1396875812.334406.jpg

    Expressions which I used where

    V(r)= k q/r

    Where q= σ da

    Where da is an element of area

    And k= 1/4πε

    I messed around with these expressions for a while but it didn't really go anywhere I was having trouble defining and element of area (to use spherical coordinates or not).

    Any help or suggestions would be great thanks in advanced :):):):)
  2. jcsd
  3. Apr 7, 2014 #2
    What area? It is a ring. You can consider linear charge density.
  4. Apr 7, 2014 #3
    Ok so area of the circle is


    And if I'm assuming linear charger density my equation would become

    V(r)= k λ/r dl
  5. Apr 7, 2014 #4
    Do you realize that you will have to integrate over the ring? Have you done any similar problems?
  6. Apr 7, 2014 #5
    Yea I realise that but I haven't had a similar problem, most problems have been on the xy plane alone
  7. Apr 7, 2014 #6
    Oh, just now I realized that your point A is on the z axis.
    There is an "a" in the xy plane that misled me.

    Then is is much simpler than I thought.
    If you take a small element of ring with length dl, what will be the charge on this element?
    What will be the distance between this element and the point A?
  8. Apr 7, 2014 #7
    What I mean is it was a two dimensional problem where lines were the only consideration rather than areas or volumes
  9. Apr 7, 2014 #8
    Oh, here it's the same too. It has nothing to do with areas or volumes.
  10. Apr 7, 2014 #9
    The distance between the two points would be

    (z^2+ x^2)^1/2
  11. Apr 14, 2014 #10
    Would I just use my distance and integrate from -a to a, or rather multiply by 2 and integrate from 0 to a?
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