Real and Virtual Images by a Plane Mirror

A plane mirror does not always form a virtual image. When a real object sends out ordinary divergent rays, reflection off a plane mirror still leaves them divergent, so they only appear to originate from a point $I$ behind the mirror -- this cannot be caught on a screen and is therefore a virtual image, the everyday case. But if instead convergent rays (a virtual object) are made to fall on a plane mirror, reflection can bring them to an actual focus at a point $I$ in front of the mirror -- a genuine real image that can be caught on a screen. This distinction between real and virtual, for both objects and images, is summarised generally: a real image is where rays actually converge; a virtual image is where rays only appear to diverge from; a real object is where rays actually diverge from; and a virtual object is where rays only appear to converge towards -- this fou …