Calculating the electric field

  1. 1. The problem statement, all variables and given/known data

    What are the strength and direction of the electric field at the position indicated by the dot in the figure?

    [​IMG]

    2. Relevant equations

    Edipole = ~ [1/(4πε0)] * [2p/r3 ]
    on the axis of an electric dipole

    Edipole = ~ [-1/(4πε0)] * [p/r3 ]
    in the plane perpendicular to an electric dipole

    3. The attempt at a solution

    Which equation should I use??

    Thanks
     
    Last edited: Oct 5, 2007
  2. jcsd
  3. Avodyne

    Avodyne 1,277
    Science Advisor

    Neither. Your equations only apply if the two charges in the dipole are much closer together than the distance r from the dipole.
     
  4. what formula would i use?
     
  5. my textbook uses these forumulas...so i tried the problem using them

    so here is my process:

    p = qs

    s=0.1
    q=1*10-9
    p=1*10-10

    1/(4πε0) = 9*109

    r=0.05m

    plugging everything into the second equation {[-1/(4πε0)] * [p/r3 ]}, i get -7200, but this is incorrect
     
  6. nicksauce

    nicksauce 1,275
    Science Advisor
    Homework Helper

    Why not just use coulomb's law, and superimpose the two electric fields?
     
  7. good idea..this was my original approach, which didn't work for some reason

    E=[1/(4??0)]*[q/r2]

    using the two charges:

    q1=1*109
    q2=-1*109

    and their respective distances:

    r1=0.05
    r2=0.01250.5 (square root)

    and doing all calculations, and then adding the two charges (3600 and -720) gives me 2880, which is incorrect...
     
  8. lol so yea....umm...any help?
     
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