Question

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

• A. $3d$
• B. $\frac{d}{2}$
• C. $d$
• D. $2d$

Answer 1

The correct option is A $3d$

By similar triangles, $\Delta AEC\approx \Delta IHA$

$\frac{y}{2L}=\frac{d}{2L}$

$y=d$

Total distance, CD = $y+\frac{d}{2}+\frac{d}{2}+y=3d$