Question-Electrostatics-Point charge and uncharged plate

[GPhab]

Homework Statement

A point charge is placed at a distance "d" from a huge uncharged metal (slab or plate).[Comment: I'm not sure. Work out both cases]. Calculate the force with which the charge attracts the plate.

Homework Equations

The Attempt at a Solution

The field inside the slab is zero. Imagine a plate and a point charge (say +Q) is placed to its right. A negative charge appears on the side facing the charge and positive charge on other side. Calculating the charge density is not a problem. As the field due to plates of charge doesn't vary with distance(they are small compared to the dimensions in this case), there is no net field due to the positive and negative induced charge surfaces at the place where the point charge is. So the point charge won't experience any force. But we were told that the force IS NON-ZERO. For the plate case, the positive and negative induced charges are at the same place and the force is zero. Help!

 

[GPhab]

Sorry. I found that this is a standard example demonstrating some technique called "method of images".