# Electric Field within Cylinder

1. Nov 13, 2008

### hoarhaykoobas

Electric Field within Cylinder - Gauss's Law

Hi, I am new to this forum. I am dying over this problem. Any help would be greatly appreciated.

1. A long cylinder has a uniform fixed charge density $$\rho=-8.3\times 10^{ - 7} C/m^3$$. The region outside the cylinder carries no charge. The radius of the cylinder is 0.024m.
(a) What is the electric field at a position inside the cylinder marked "x" which is 0.017m away from the center line of the cylinder? A: -800 N/C
(b) What is the electric field at a position outside the cylinder marked "y", which is 0.035m away from the center line of the cylinder? A: 770 N/C

2. Gauss's Law: $$\phi= \frac{\sigma A}{\epsilon_{0}}$$

3. The closest I got to the answer to part (a) is as follows:$$\\ Q=\rho\times A\times d=-5.11\times 10^{-11}$$$$E=K_{e}\frac{Q}{r^2}=-797.55 N/C$$
Part (b) i just can't seem to apply the same method, which i believe is pretty flawed to begin with.
*My textbook doesn't cover this too deeply and my professor gave this to us as a supplemental problem.

After getting nowhere with the electric flux equations and it's diff forms for part (b), I found this page, which seemed to be exactly what I was looking for but i keep getting the wrong answer: http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elecyl.html" [Broken]

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Last edited by a moderator: May 3, 2017
2. Nov 13, 2008

### G01

Gauss's Law is the correct way to do this problem. Can you show your work? I cant find you mistakes if I can't see your work.

3. Nov 13, 2008

### hoarhaykoobas

I updated my question. I'm sorry about that. I hope it's easy to see what I'm doing wrong. I've included a jpeg of the problem. Thanks so much