Electric Potential in a Conductor

1. Sep 29, 2005

saugei

#1. We have a hollow metal spherical shell with charge -q and with radius rb
#2. We have a soild metal sphere supported by an insulating stand with charge +q and radius rb
#3. The solid metal sphere is located in the center of the hollow metal spherical shell (aka. #2 is in #1)
The question asks me to calculate the potential, V(r) when:
A. r < ra
B. ra < r < rb
C. r > rb

The solution:

A. k*[(q/ ra)-(q/ rb)] where k= 1/(4*pi*epsilon_0)

C. k*[(q/r)-(q/r)] = 0

What I don’t understand:

A. The electric field in #2 is 0; hence the electric potential should be constant. So, I would think that the potential of r < ra should be V=k*(q/ ra) because it is telling us to find the potential inside of ra which should be a constant throughout the solid sphere. Right? Then how come the answer gives me the sum of the electric potential for #1 and #2??

C. I got totally lost at part C any clue please?

Last edited: Sep 29, 2005
2. Sep 29, 2005