question_answer

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- [JEE Main 12-Jan-2019 Morning]

A) 3d

B) 2d

C) d

D) \[\frac{d}{2}\]

Correct Answer: A

Solution :

[a] In the given figure and are similar triangles.

So,             (i)

Also, and are congruent triangles.

So, ED = DS                                                                 ...(ii)

Using (i) and (ii), BC = d

So, the distance over which the man can see the image of the light source in the mirror is