How Do Electric Fields Differ Between Aluminum and Glass Plates?

[jesuslovesu]

Homework Statement

A very large flat aluminum plate of area A has a total charge Q over its surface. The same charge is placed over the upper surface of a glass plate. Compare the electric fields.

Homework Equations

The Attempt at a Solution

I know how to get the electric field of the aluminum plate.
$$\sigma$$ = Q/A
2EA = $$\sigma$$A/e0
E = $$\sigma$$/2e0

For the glass plate, I'm not so sure... Initially I would think E = $$\sigma$$/e0, but it isn't...

 

[Doc Al]

Realize that the aluminum plate is a conductor.