# Homework Help: Gauss's Law Problem

1. Oct 13, 2008

### bcjochim07

1. The problem statement, all variables and given/known data
A long, thin straight wire w/ linear charge density lambda runs down the center of a thin, hollow metal cylinder of radius R. The cylinder has net linear charge density of 2lambda. Assume lambda is positive. Find an expression for the electric field strength inside the cylinder.

I used a cylinder of length L for my gaussian surface:

the charge inside is lambda * L

E*2pir*L = lambda * L / permittivity constant

E= lambda/ (2pi*r*permittivity constant)

This is correct, but the thing I don't see is how the electric field from the metal cylinder cancels inside the cylinder. Wouldn't it only cancel at the very center?

2. Relevant equations

3. The attempt at a solution

2. Oct 13, 2008

### bcjochim07

Oh... if I draw a gaussian surface inside, it only encloses the wire. I'm trying to fit my head around this.

3. Oct 13, 2008

### bcjochim07

Could someone please give a good explanation for this? Thanks

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