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Question:

A point source of light, S is placed at a distance L in front of the centre of a 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 :

3d

d/2

2d

d

Solution:

The correct option is A
3d
By similar triangles, ΔAEC ≈ ΔIHA
y/2L = d/L
y = 2d
Total distance, CD = y + d/2 + d/2 + y = 3d