A point source of light S, placed at a distance 60cm in front of the… | JEE Main 2021 (26 Feb, Shift 2)

Q36JEE Main 2021 · 26 FEB · SHIFT 2Difficult

Reflection & Mirrors

A point source of light S, placed at a distance 60cm in front of the centre of a plane mirror of width 50 cm, hangs vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror at a distance 1.2 m from it (see in the figure). The distance between the extreme points where he can see the image of the light source in the mirror is __________ cm.

Numerical answer type. Work it out, then open the answer.

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Answer: 150

Image $S'$ is 60 cm behind the mirror; rays from $S'$ through the mirror edges reach the man's line.
Distance of the man's line from $S'$ : $60 + 120 = 180\text{ cm}$ = 3 times the mirror's distance from $S'$ .
Visible stretch $= 50 \times \frac{180}{60} = 150\text{ cm}$
So the answer is 150 cm.

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Reflection & Mirrors question from JEE Main 2021 (26 Feb, Shift 2)

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