# Homework Help: Electric Potential Problem

1. Feb 28, 2008

### Seda

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

A co-axial consists of .002m diameter inner conductor and an outer conductor of .016m diameter (thickness is negligible). If the conductors carry line charge densities of +/- 5.6*10^-10 C/m, what is the magnitude of the potential difference between them.

2. Relevant equations

I know that the electric field for any continuous cylindrically symmetric charge distribution with linear charge density L

E= L/(2*pi*constant*r)

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I know that the electric field at the surface of any conductor is (Surface charge density)/constant.

I Know that Potential= -SE* dl

S is integral sign.

Constant is the permutivity constant, I don't know how to put the symbol on here.

3. The attempt at a solution

Well I know that the magnitude of the electric potential outside of any line of charge

E= L/(2*pi*constant) times ln(rb/ra) where rb is radius outside line and ra is the radius of the distribution. Its the fact that the outside radius in this case is also charge which is throwing me off

2. Feb 29, 2008

### michalll

It may help you that inside long cylinder with homogeneous charge density E=0.