1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Three concentric shells, one uncharged (Potential)

  1. Sep 28, 2011 #1
    1. The problem statement, all variables and given/known data

    See figure attached.

    2. Relevant equations

    3. The attempt at a solution

    See figure attached for my attempt.

    I'm confused as to how I am supposed to use these 3 electric fields, E1, E2 and E3, as well as the potential of the middle shell, V = 1kV (with reference point at infinity), to calculate the charge on the middle shell, [tex]q_{mid}[/tex]

    I know I should be doing some integration over the electric fields in order to get the potential, but it's not obvious to me what path I should take to only have the potential of the middle shell.

    The solution gives it as from c to d, and then from e to infinity.

    Why so?

    Can someone clarify? Is the picture I drew incorrect?

    Thanks again!

    Attached Files:

  2. jcsd
  3. Sep 30, 2011 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    You wrote an expression for the field inside the middle shell which you know can't be right, since the E field inside a conductor is zero.

    But you have the right idea in using Gauss' theorem. Use it for the spaces between the shells, and integrate the E fields accordingly to get the potentials. Call the charge on the middle shell Qb for the moment.

    Then, you need to compute Qb given the middle shell's potential as 1 kV. Careful how you do this, it isn't just kQb/Rbo where k = 9e9 and Rbo is the outer radius of the middle shell (why not?).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook