1. Not finding help here? Sign up for a free 30min 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!

EM 2 parallel plate

  1. Sep 23, 2007 #1
    2 infinite parallel plates separated by a distance s are at the potentials zero and V0.
    find the surface charge densities on the plates.

    I got the answer that it first calculate E and then as

    1. x=o, Ex = σ / ε, then could know σ
    2. x=s, Ex = - σ / ε ---> here's what I don't know. why there's a minus sign here ?

    Thank you so much ~
     
  2. jcsd
  3. Sep 23, 2007 #2
    There's another question in EM.

    the original question is like below :

    consider a spherically symmetric charge distribution ρ = ρ(r). By dividing the charge distribution into spherical shells, find the potential and the eletrica field strength in terms of ρ(r)

    I got the answer that it first consider it as charge only on a shell with radius r', get E and V in terms of σ, then infintely many this kind of shells build a sphere with charge density ρ(r), and then it shows that :

    σ =[ 4π (r')^2 dr' ρ(r) ] / 4π (r')^2 = ρ(r') dr' = σ(r')

    I don't get this. how come would have this equation ?
    it seems σ(r') should be : total charge / surface area, and shouldn't total charge be
    (4/3) π (r')^3 ρ(r) ?

    Thank you.
    σ =
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: EM 2 parallel plate
  1. Parallel Plates (Replies: 5)

  2. Parallell plates (Replies: 2)

Loading...