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 in the figure. 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

The correct option is D $3d$

The reflection from the top and bottom of the mirror will be the two extremes at which the spot B can be seen.

The diagram is self explanatory. As B to mirror is half of mirror to screen, the vertical distance for which light B is seen below the mirror length is twice of vertical distance B and bottom of mirror $=2\left(d/2\right)=d$

Similarly visibility above mirror is for length $d$

Visibility throughout mirror $=d$

Total range of visibility $=d+d+d=3d$