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: Electric field and potential difference in coaxial cable

  1. Jan 12, 2009 #1
    Consider a coaxial cable with inner radius a and outer radius b. The potential difference between the inner and outer conducter is V. How can it be shown that the electric field at a distance r from the inner conducter is given by:

    E = \frac{V}{r ln\frac{b}{a}}

    Any help would be much appreciated!
  2. jcsd
  3. Jan 12, 2009 #2
    Let the inner conductor of radius a have a charge +Q and the outer conductor at radius b have a charge of -Q. Use a cylindrical Gaussian surface to calculate the electric field, E, at any point inside the cable. This will give E = Q/(εA) where A = 2*pi*r*l and l is a unit axial length. Then find V by finding the integral of E dot dr. This will give V = Q/(ε*2*pi*l)ln(b/a). But Er = Q/(ε*2*pi*l) so V = Er*ln(b/a). Solving for E gives shows the desired expression for E.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook