A point source of light S, placed at a distance 60 cm infront of the centre of a plane mirror of width 50 cm, hangs vertically on a wall. A man walks infront of the mirror along a line parallel to the

Question

A point source of light S, placed at a distance 60 cm infront of the centre of a plane mirror of width 50 cm, hangs vertically on a wall. A man walks infront 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.

TestHub · Accepted Answer

Image of S is 60 cm behind the mirror; the man walks on a line $60 + 120 = 180 cm$ from the image.

By similar triangles, half the visible span = $25 \times \frac{180}{60} = 75 cm$ .

Full span = $2 \times 75 = 150 cm$ .

Answer: 150

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