# Homework Help: A question in static charge

1. Aug 13, 2013

### Ammar Qasim

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

2. Relevant equations

3. The attempt at a solution
I think it depends on induction so when the rod is brought close, the spheres will be positively charged. When they move away of it, A will get a negative charge "by induction" and B will get a positive one

2. Aug 13, 2013

### Staff: Mentor

Hi Ammar Qasim, Welcome to Physics Forums.

Since the spheres are on insulated stands and the rod never contacts the spheres, charges can only move around, and no new charges will enter the system (conservation of charge). The two spheres start out neutral (zero net charge). Further, charge can only move where there is a conduction path. What does this tell you about the sum of the charges on the two spheres after they are made separate?

When the spheres are in contact and the rod is brought close, make an approximate sketch of the distribution of charges on the spheres. What will it look like?

3. Aug 13, 2013

### Ammar Qasim

Hi gneill, thank you for help.
When rod is brought close the positive charge will move to A and the negative charge will move to B then A will be attracted to the rob holding the positive charge so the answer will be letter B. Did I get it ?

4. Aug 13, 2013

### Staff: Mentor

No. What happened to the negative charge that you say moved to B? Where does it go if you say that sphere B ends up neutral while sphere A is positive?

Last edited: Aug 13, 2013
5. Aug 13, 2013

### Ammar Qasim

Oh, you are right. the negative charge will remain at B so the answer will be letter (A)

6. Aug 13, 2013

Looks good