A plane mirror having a square shape is mounted parallel to a vertical wall at some distance from it. A point light source is fixed on the wall. Light from it gets reflected from the mirror and forms a patch on the wall, when the mirror is moved parallel to itself towards the wall-

If the mirror is moved parallel to itself  with velocity along the line, normal to wall and passing through the source, then patch will remain unchanged in shape but since angle of incidence of incident rays at the edge of the mirror gradually increases, size of the patch gradually increases.