# Work Done by an Insulating Sphere on a test charge

1. May 20, 2013

### tyler3902

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

An insulating sphere of radius 0.240 has uniform charge density 6.50×10−9 . A small object that can be treated as a point charge is released from rest just outside the surface of the sphere. The small object has positive charge 4.10×10−6

How much work does the electric field of the sphere do on the object as the object moves to a point very far from the sphere?

2. Relevant equations

3. The attempt at a solution

I tried to use kQq/r to find the work done but I'm honestly very lost about where to start.

Any help is extremely appreciated, thanks.

2. May 20, 2013

### Dick

You've got the right formula, now use it. You can treat the sphere as a point charge concentrated at the center of the sphere. What's the total charge of the sphere?

3. May 21, 2013

### tyler3902

would it be the charge density multiplied by the surface area of the sphere?, so 4/3pir^3(6.5x10^-9)?

4. May 21, 2013

### Dick

4/3pir^3 is the volume of the sphere, not the surface area. But I still think that's the correct thing to do. If it's an insulating sphere they probably gave you the volume density not the surface density.

5. May 21, 2013

### tyler3902

bleh stupid me, appreciate all the help Dick :)