Since the refracted rays are diverging, they will not come to a focus at any point.
To an observer's eye located at the right, however, such rays will appear to be coming
from the common point Q'. In other words, Q' is the image point corresponding to
the object point Q. Similarly M' is the image point corresponding to the object point
M. Since the refracted rays do not come from Q' but only appear to do so, no image
can be formed on a screen placed at M'. For this reason such an image is said to be
virtual.