Electric Field Magnitude of Cylinder w/ Uniform Charge

[radiocool]

So question :
We have cored cilynder. Inner radius 10 cm, outer radius 20 cm. In the walls
of the cilynder uniformed charge 2nK/m^3. Find electric field magnitude at the points from axes 8cm 18cm 28cm.

Sorry for my english.

 

[neutrino]

I think you mean 2 nC/m^3 for the charge density. What attempts have you made in solving this problem. The first case is the easiest.

 

[radiocool]

Yes I mean nC/m^3. So For 8cm I think to use that E = <r0>*r\(2*e*0e).
it is a case then point where we define electric field is inner cilinder.
But then we have 18cm, then point would be in the cilinder.
3 case i could use E = <ro> *R^2\(2*e0*e*r), but what should be R - radius od cilynder 20cm.

<ro> is charge density.

 

[neutrino]

For the first case, the gaussian cyclinder would enclose no charge at all. Now for the other two, draw similar gaussian cylinders - one within the walls and the thrid outisde the charged cylinder. If you know the general case of evaluating the field of a long cylinder using Gauss' law, it would be a simple exercise to solve the problems.

 

[neutrino]

EDIT: Never mind...I was being an idiot!

 

[radiocool]

For the first case, the gaussian cyclinder would enclose no charge at all. Now for the other two, draw similar gaussian cylinders - one within the walls and the thrid outisde the charged cylinder. If you know the general case of evaluating the field of a long cylinder using Gauss' law, it would be a simple exercise to solve the problems.