Question

A point source of light $B$ is placed at a distance $L$ in front of the centre of a mirror of width $d$ hung 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)

According to the following ray diagram $HI=AB=d$

and $DS=CD=\frac{d}{2}$
$AH=2AD$
$\Rightarrow GH=2CD=\frac{2d}{2}=d$
Similarly $IJ=d$ so $GJ=GH+HI+IJ$
$=d+d+d=3d$