Q: 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) 2 d
(D) 3 d
Ans: (d)
Sol: 
As triangle ΔS’AB & ΔS’PQ are similar
$\large \frac{d}{PQ} = \frac{L}{3L} $
PQ = 3 d