Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Surface bound charge on the outer surface of a dielectric

  1. Oct 25, 2017 #1


    User Avatar

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

    With regards to a one dimensional conducting wire with a homogeneous charge density λ surrounded by a cylindrical glass dielectric of radius R, find:

    (a). The displacement vector inside the dielectric

    (b). The surface bound charges on the surface of the dielectric

    Sorry for the lack of equations and mathematical explanation. Trying to put everything mathematically and graphically would have been quite long. Rest assure I have everything that I'm describing in the attempt written in the correct notation on paper.

    2. Relevant equations

    Included in attempt

    3. The attempt at a solution


    Drawing a cylindrical Gaussian surface inside the dielectric of radius r and length L.

    Surface integral (displacement vector, D) dot product dS (differential of surface) = charge enclosed

    dS = 2πr L

    Qenc= λ L

    ⇒ surface integral D (2πr L) = λ L

    D = λ/2πr

    For the displacement vector D(bar) = λ/2πr r(bar)


    I'm slightly confused as to where to approach this one from:

    D(vector) = εE(field vector) + P(vector)

    E and P are the electric field and dipole moment.

    Surface bound charge = σ = P(vector) n(normal vector)

    σ = σbound + σfree

    From here on I don't really know how to approach this problem. Apologies for the scrappy attempt.
  2. jcsd
  3. Oct 25, 2017 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    OK for part (a)

    For part (b) try to make use of either the dielectric constant of the glass or the electric susceptibility of the glass.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted