Main Question or Discussion Point
Hello! I am reading about image charges for an infinite plane and a charge above the plane. In the book I am reading (Griffiths) the author says (and uses this results several times) that the field below the plane is 0. How do we know this? The method of the mirror charges gives the V above the plane only, so how do we know anything about the electric field below i.e. why is it obvious it is 0?