# Conductors and Gauss Law

• -EquinoX-

## Homework Statement

http://img21.imageshack.us/img21/8079/orderyy3.th.jpg [Broken]

## The Attempt at a Solution

Well all I know that the smallest will be C, as it's 0 (inside the conductor), I think the next one is A, and I don't know about B and D

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Inside the inner shell at A is 0, as for B and D which one is farther away from the charge source?

so A and C are both 0? D is farther... but flux isn't associated with radius isn't it

Imagining a Gaussian sphere enclosing the charge as far out as A, it would have less charge than a sphere at B.
The field at D will be smaller than B because it is spread out more in space.
Pretty tough to compare A and D.

I don't know how this works. What makes E = 0 in the conducting layer? It seems to me that the field due to the central charge would cause a charge separation in conducting layer C, so that (assuming central q is positive) there will be a layer of negative charge on the inner side of layer C and a positive one on the outer side. Do you know if that is correct?

E = 0 in the conducting layer because the electric field is 0 inside the conductor

What makes E = 0 in the conducting layer?

If there were an E-field inside the conductor ... and the electrons are free to move ... how can an E-field be maintained?

Here's a lecture that covers this and more on electrostatics:

(about 20 min in. Though the whole lecture is good.)

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If there were an E-field inside the conductor ... and the electrons are free to move ... how can an E-field be maintained?

Here's a lecture that covers this and more on electrostatics:

(about 20 min in. Though the whole lecture is good.)

Therefore I was right that there is no E field inside the conductors right?

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Yes, there should be no E-field inside a conductor, therefore the charge enclosed by a Gaussian surface drawn inside a conductor should be zero.

Inside the inner shell at A is 0, as for B and D which one is farther away from the charge source?

The inner shell isn't zero, because it's an insulating shell instead of conducting, so charge is distributed uniformly.

The inner shell isn't zero, because it's an insulating shell instead of conducting, so charge is distributed uniformly.

If the point A is inside the shell - shell being the operative word - and inside of that then, it is 0. If it were a solid sphere with uniformly distributed charge, you would be correct (if A is not the center). But they call it a shell.

So what is the charge on A then?

If the point A is inside the shell - shell being the operative word - and inside of that then, it is 0. If it were a solid sphere with uniformly distributed charge, you would be correct (if A is not the center). But they call it a shell.

Hmmm...this problem is certainly open to some interpretation!

If it is indeed a shell, and if A is inside the shell; even that doesn't guarantee the field is zero inside. Charge isn't free to distribute itself on an insulator, so there is no guarantee that the charge Q is uniform over the insulating shell. If it isn't uniform, then the field will not be zero.

I suspect that you are to assume that the charge Q is not distributed uniformly over the shell, and that the point A is very close to the charge, producing a large field at A. But that's just a guess.

@EquinoX--- You should probably ask for clarification from your prof or a TA.