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 fig. The greatest distance over which he can see the image of the light source in the mirror is

Options

A. `(d)/(2)`
B. `d`
C. `2d`
D. `3d`

Answer

D

Explanation

The image of B i.e., `B^(')` will be visible to man when he is moving between `P` and `Q` i.e.over distance PQ.
In similar Delta, `B^(')JK` and `B^(')QP`
`tantheta=(d)/(L)=((PQ=d^(')))/(3L)`
`PQ=d^(')3d`