# Homework Help: How to use Gauss's Law to determine charge on a cylidrical shell w/ a defined length?

1. Jan 30, 2013

### Klymene15

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

"A cylindrical shell of length 230 m and radius 6 cm carries a uniform surface charge density of σ = 14 nC/m^2. What is the total charge on the shell? Find the electric field at the end of a radial distance of 3 cm from the long axis of the cylinder."

2. Relevant equations

Gauss's Law
Volume of a cylinder=∏r^2*h

3. The attempt at a solution

The textbook hints that it has something to do with Gauss's law. As I searched for hints online, I only found answers with cylindrical shells with infinite lengths. The fact that we still haven't covered Gauss's Law in class (this is due tomorrow at noon), probably doesn't help either.

So maybe... a quick, crash course on how I'm suppose to use Gauss's Law for a problem like this, and how to do it? The set up, at least?

2. Jan 30, 2013

### rude man

Re: How to use Gauss's Law to determine charge on a cylidrical shell w/ a defined len

The question doesn't tell you how far along the length of the shell the observation point is, and seems to me that matters. But if its 3 cm from the middle of the shell (i.e. 115m from either end) then Gauss's law can be applied to compute the E field as described.

3. Jan 30, 2013

### haruspex

Re: How to use Gauss's Law to determine charge on a cylidrical shell w/ a defined len

It says "Find the electric field at the end of a radial distance of 3 cm from the long axis". Not very clear, but it sounds to me that it is at the end of the cylinder, 3cm from the axis. (Otherwise, why bother to specify the length?)

4. Jan 30, 2013

### rude man

Re: How to use Gauss's Law to determine charge on a cylidrical shell w/ a defined len

Confusing statement still. "At the end" could mean at the end of the radial distance or the end of the cylinder. "At the end OF ... " doesn't sound like they meant the end of the cylinder to me.

The length still matters unless you're at the center of the cylinder, axially speaking.

BTW I think this is intended to be a trick question.