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: Electric potential in regions of concentric thin, conducing, spherical shells

  1. Feb 3, 2004 #1
    two thin conducting spherical shells as shown below. the inner shell has a radius of r1=15.0cm and a charge of 10.0nC. the outer shell has a radius r2 = 30.0cm and a charge of -15.0nC. find the electric potential V in regions R1, R2, and outside the outer shell, with V = 0 at r = infinite.
    s0219.gif
     
  2. jcsd
  3. Feb 3, 2004 #2
    What is the expression for Potential due to a Spherical shell

    In General

    [tex] V=\frac{Q}{4\pi \epsilon_0 R} **&\mbox{for}** r \leq R[/tex]

    AND

    [tex] V=\frac{Q}{4\pi \epsilon_0 r} **&\mbox{for}** r \geq R[/tex]
     
    Last edited: Feb 3, 2004
  4. Feb 3, 2004 #3
    I disagree with the above equations. From Gauss' law, a spherical shell does not contribute at all to the potential inside it--it's easier to think about with gravity: if the earth were hollow, you could float around in it; you wouldn't be attracted to any point on the shell.

    So if you're inside the shell, you don't see it; if you're outside the shell then (again by an application of Gauss' law) it affects you in the same way that a concentric point charge of the same total charge would, i.e., a one over R potential.

    That should get you started; you treat two shells with the superposition principle (i.e., add the two potentials together.)

    P
     
  5. Feb 3, 2004 #4
    WHY it is not true

    => 0 which is not true.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook