00:01
Okay, we have a cylindrical rod of a conductor.
00:05
We have surrounding that a cylindrical shell that's very thin.
00:10
We're told the electric field outside is zero.
00:14
We're told that there's a charge density sigma per unit area on the outer shell.
00:22
So the first question is, is there charge on the rod? and the answer is yes.
00:28
It does have a surface charge density that's minus b over a times.
00:32
This sigma on the outer shell, which ends up to be this, might be over a times sigma.
00:40
The reason we know that is true is because the electric field is zero outside, which means that if we take a gaussian surface that's entirely outside of this, the flux has to be zero, which means the charge enclosed has to be zero, so that the total charge on the outer conductor has to to be the negative of the total charge on the interconductor.
01:07
And so that gives us this relationship that tells us the surface charge density on the interconductor.
01:16
For part b, we know that the interconductor is a rod...