Induced Charge on a Conducting Disk

[cardsfan527]

Homework Statement

A large, thin plastic disk with radius R = 1.1 meter carries a uniformly distributed charge of Q = -7e–5 C. A circular piece of aluminum foil is placed d = 3 mm from the disk, parallel to the disk. The foil has a radius of r = 6 cm and a thickness t = 1 millimeter.

a. Find the net electric field at the center of the foil.
b. Calculate the magnitude q of the charge on the left circular face of the foil.

Homework Equations

E = 1/(4*∏*ε)*q/r^2

The Attempt at a Solution

I know that the answer to part (a) is 0, because a conductor will not have an electric field inside of it.

I also know that the charge on one side of the foil disk will be equal and opposite to the charge on the other side, since the disk has a neutral total charge. I'm just unsure of exactly where to go from there. Should I use force equations, since I know that the charges are at rest? Or is there something I know about the electric field that I can use?

 

[Goddar]

Hi.
So you have a zero field inside the conductor, and non-zero right outside. Determine the field outside, remember the formula for induced surface charge density, then integrate over the surface...

 

[cardsfan527]

Thanks, Goddar. I guess my problem is calculating the electric field. Could you send me in the right direction?

 

[Goddar]

Method of images, since the disk is "large"...