# Homework Help: Potential difference?

1. Sep 13, 2011

### Juggernaut

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

Assume we have cavity in conductor. In the cavity we have +3q charge and conductor charge is distributed uniformly and is +7q.
With Gaus law we now that E=0 inside the conductor becaus Q enclosed is 0. But I have been wondering is there potential difference from inner wall to outer wall of conductor?
There is -3q in the inner wall and +4 outer wall and inside conductor E=0 so V= constant but is there potential leap between inner and outer wall?

2. Relevant equations

3. The attempt at a solution

2. Sep 13, 2011

### Hootenanny

Staff Emeritus
What makes you say that there is a potential difference?

3. Sep 13, 2011

### Staff: Mentor

I can't help with this, but I am trying to picture it. The charge distribution on the outside of a block of aluminium I can visualize. And I can picture a hole being drilled into the block. But how are you going to keep those 3q charges inside the hole? It's a conductor, so they will succeed in migrating to the outside and distributing themselves apart from the others.

These are static charges? Then I think there can be no potential difference between any two points on the conductor; the charges are free to move to reposition themselves so that all points on the surface of the conductor are at a uniform potential.

4. Sep 13, 2011

### Hootenanny

Staff Emeritus
It is not only the actual charge that is important, but the charge density on each surface. The outer surface is naturally larger and thus will require a greater total charge in order to have the same charge density as the inner surface, thus maintaining a zero field inside the conductor.

5. Sep 13, 2011

### Juggernaut

well asume the conductor is spherical, and theres sphrical cavity in it. charge +3q in its origo, inner wall of conductor is 0-->a and outer wall is 0-->b.

well if u draw Gaussian surface around the charge in the cavity then E is not zero, r<a, then thered be potential difference inside the cavity, but if u draw GS a<r<b theres not. So I am thinking that just before the inner surface theres different potential than outside the conductor due to different charge of the surface...I know I explained it very hard way...Can I post here a picture?

E: Yes I can!

Last edited: Sep 13, 2011
6. Sep 13, 2011

### Juggernaut

heres the picture!!!! as you can see I am next Da Vince :D

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