Question

A point source of light S, placed at a distance L in front of the centre of a plane mirror of width d, hangs vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror at a distance 2L from it as shown. The greatest distance over which he can see the image of the light source in the mirror is

• A. d/2
• B. d
• C. 2d
• D. 3d

Answer 1

Answer: (D)

3d

Answer 2

The ray diagram will be as follows :
HI=AB=d
DS=CD=$\frac{d}{2}$
Since, AH = 2AD
\therefore \hspace15mm GH=2CD=2\frac{d}{2}=d
Similarly, IJ = d
\therefore \hspace15mm GJ = GH + HI + IJ
= d + d + d = 3d