# Finding E fields and potential given a hollow spherical conductor

1. Jan 23, 2013

### SeanLikesRice

Hello, this is my first post here, so hopefully I do this in the right way...

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

A hollow spherical conductor carries a net charge of 21.5 μC. The radius of the inner hollow is 5.2 cm and thee full radius of the sphere is 7.8 cm. At the center of the sphere, in the middle of the hollow, is a point charge of -12.2 μC.

Find the E field at a distance of 8.0 cm from the center of the sphere.

2. Relevant equations

$E = \frac{kQ}{r^2}$

3. The attempt at a solution

Now when I draw this up in my notebook, I'm a little confused. Since the conductor has a net charge of 21.5 μC, does the point charge of -12.2 μC not matter in terms of finding the E field?

Using the net charge...

$E = \frac{k * 21.5μC}{(8.0cm)^2}$

Is this correct, or d I have to account for the point charge in the center of the hollow sphere?

2. Jan 23, 2013

### haruspex

Think about the distribution of charge on the conductor. What will the charge be on the inside surface?

3. Jan 24, 2013

### rude man

What does Gauss say? Does he say it matters how the charge inside his surface is distributed?