What is the Charge on the metal plate?

[loganblacke]

A metal plate is connected by a conductor to a ground through a switch. The switch is initially closed. A charge of +Q is brought close to the plate without touching it, and then the switch is opened. After the switch is opened, the charge +Q is removed. What is the charge on the plate then?

Homework Equations

The Attempt at a Solution

This is all new to me, I have no clue.

 

[andonrangelov]

The plate will have the same charge but opposite sign. For more details see the Method of images (for example here http://en.wikipedia.org/wiki/Method_of_images)...
Of course this is if you assume that the metal plate is infinity big (the charge is close to the plate surface)
Sorry better this link http://en.wikipedia.org/wiki/Method_of_image_charges