# Finding electric potential between two concentric spheres.

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1. Mar 18, 2017

### epicrux

1. The problem statement, all variables and given/known data
A spherical shell with inner radius A and outer radius 3A which has a uniform charge density, i.e charge per unit volume, p0. Find difference in electric potential between the center of the shell and a point a distance 2A from the center.

2. Relevant equations

3. The attempt at a solution
I am completely lost as to what I'm supposed to do here. I would think you'd find the potential at 2A and subtract it from that at the center. But how exactly do you do that?
I integrated the elctric field due to a charged sphere along 2A to A. So that makes:
∫E dr= ∫(ρr)/3ε0)dr=V
That makes:

[(ρr2)/6ε)] from 2A to A which does not equal the answer.
I think I'm stumped here. Any help would be greatly appreciated!

2. Mar 18, 2017

### TSny

Welcome to PF!

Your expression for the electric field does not look correct. E for a uniformly charged shell is different than E for a uniformly charged solid sphere.

3. Mar 18, 2017

### epicrux

I was not aware of the difference. I'll look it up.

4. Mar 18, 2017

### TSny

Or, apply Gauss' law to find E inside the shell.