A point source of light P is placed at a distance L in front of a mirror of width d hung vertically on a wall . A man walks infront of the mirror a long a line parallel to the mirror at a distance 2L as shown in the figure. The greatest distance over which he can see the image of the light source, in the mirror is

Explanation

Locate the position of image and by the help of shortcut method of locating field of view join the mirror through lines, and that region is the field of view then, by similar triangle concept the triangles IPQ and IMN are similar,
`(PQ)/(MN)=(3L)/L implies PQ=3d`