# Homework Help: Voltage not zero at infinity

1. Feb 3, 2012

### jehan60188

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

A point charge q = -8 µC is surrounded by two thick, conducting spherical shells of inner and outer radii a1 = 0.2 m, a2 = 0.3 m, a3 = 0.8 m, and a4 = 0.9 m respectively. The inner shell is uncharged; the outer shell has a net charge Q = -8 µC. At this point in the problem, the potential at infinity is unspecified. Do not assume it is zero.

If now you are given V(inf) = 1 x 105 V, find the potential at r = 0.1 m.

2. Relevant equations

V = ∫E*dr

3. The attempt at a solution

voltage from .1 m to .9m = -359672 + -149863 = -509535
(known from previous steps)

I have no idea how to get the voltage from .9m to infinity!

2. Feb 4, 2012

### tiny-tim

hi jehan60188!

the voltage difference from .9m to infinity is the same as it would be if the voltage at infinity was 0

3. Feb 5, 2012

### jehan60188

kk, since the voltage between point A (.9 m) and B (infinity) needs to be 10^5 higher than if it were supposed to be zero, I integrate from .9 to infinity, and then add 10^5
thanks!