# Find the value of the potential at the following distances

1. Jul 16, 2009

### Clement

1. The problem statement, all variables and given/known data
A total electric charge of 2.00 nC is distributed uniformly over the surface of a metal sphere with a radius of 20.0 cm. If the potential is zero at a point at infinity, find the value of the potential at the following distances from the center of the sphere.
(a) 48.0 cm
(b) 20.0 cm
(c) 12.0 cm

2. Relevant equations
V=(kQ)/r

3. The attempt at a solution
I got part a no problem, having difficulty with b and c
for b, when r approaches infinity, shouldn't the potential approach infinity? but infinity was not the right answer.
for c, when r is enclosed in the sphere, isn't the potential always going to be 0?

thanks

2. Jul 16, 2009

### gabbagabbahey

Hmmm... this is the potential due to a point charge isn't it....why do you think this is also true for the uniformly charged spherical surface?

$$\frac{1}{\infty}=0\neq\infty$$

Why would you say this?....When in doubt, go back to the mathematical definition of electrostatic potential...

3. Jul 16, 2009

### Clement

got it, thanks!