# Homework Help: Change in electric potential

1. Feb 6, 2009

### physicsfun

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

The diagram above shows a coaxial cable. The inner conductor has radius a = 0.0025 m. The outer conductor is a cylindrical shell with inner radius b = 0.0075 m, and outer radius c = 0.008 m from the center. Both conductors are coaxial. For every length L = 10 m of cable, there is a total charge q = 2.8e-008 C on the inner conductor and a total charge of Q = -5.6e-006 C on the outer conductor.

Determine the electric potential difference between the labeled points A and B.

3. The attempt at a solution

I'm a bit confused but I took a stab at the problem. First of all, I know that electric potential = V = kq/r...... Also, I know that since the electric field is zero within the second conductor I would essentially only be calculating the difference in electric potential between point A and the inner surface of the outer conductor. So what I did was I calculated K
*charge enclosed/r for the two points and found the difference... I can't seem to get the answer. Am I doing this completely wrong? Does q even stand for the charge enclosed? Thanks a lot for any help.... it will be appreciated greatly!

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