Homework Help: Spherical Conducting Shell

1. Sep 19, 2012

dipolarBear

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

(1)A conducting sphere w/ charge +Q is surrounded by a spherical conducting shell.
What is net charge on inner surface of the shell?

(2) A charge is placed outside the shell.
What is the net charge on the inner surface now?

(3) What if the shell and sphere are not concentric, will this change your answers?

2. Relevant equations

$$E=\frac{F}{q}$$

3. The attempt at a solution

I've done some reading from 2 different books on the same topic, and i've gotten some info from other similar problems on PF. I still feel like I need work on this section, any help is appreciated. Thanks.

(1) The inner sphere will induce a -Q charge on the interior surface of the shell, and a +Q on the outer surface.

(2) This one has me stumped: I figure that the interior surface of the shell must become -2Q with the introduction of a point charge outside. I think since its a conducting shell, the charge inside must be zero, and as a result it must create an e-field that can counter the fields of both charges, in order to remain neutral. Could I use the equation $$E=\frac{F}{q}$$, to help me solve this problem?

(3) If the sphere and shell are not concentric, the results should be the same since we're dealing with the net charge on the interior surface.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 20, 2012

voko

In (2), you seem to assume that the external charge is equal the internal. That is not how the problem is stated.

3. Sep 20, 2012

dipolarBear

Sorry, the problem uses q for the point charge outside, and +Q for the charge of the sphere. I'm not exactly sure if they're suppose to be the same, but if we assumed they were not equivalent, would the charge of the interior surface in (2) be -(Q+q)? Thanks

Last edited: Sep 20, 2012