# Homework Help: Gauss's Law problem

1. Oct 24, 2006

### chillaxin

A long straight conducting rod (or wire) carries a linear charge density of +2.0uC/m. This rod is totally enclosed within a thin cylindrical shell of radius R, which carries a linear charge density of -2.0uC/m.
A) Construct a Gaussian cylindrical surface between the rod and the shell to derive then electric field in the inner space as a function of the distance from the center of the rod.
B) Construct a Gaussian cylindrical surface outside both the rod and the shell to calculate the electric field outside the shell.

This is what i have so far.

E=q/4piEor^2
E=+2.0uC/m / 4pi8.85x10^-12(-2uC/m)^2
E=4.5x10^9Nm^2/C

2. Oct 24, 2006

### chillaxin

Anybody?!?!?!?

3. Oct 24, 2006

### OlderDan

The field is certainly not constant in the region between the rod and the cylinder. Are these anwers to multiple parts? Just the first part?

Last edited: Oct 24, 2006
4. Oct 24, 2006

### HalfManHalfAmazing

Unless I'm mistaken, the total charge inclosed in the whole system is zero. If the enclosed charge is zero, the electric field is zero. Thus from what I can draw, the answer to B is zero. The answer to A requires using the enclosed charge to be the positive portion and then solving for E.