Question

A Boy whose eyes are 150cm above the ground looks at his reflection in a vertical mirror 200 cm away. The top and bottom of the mirrors ate 220cm and 120cm above the ground respectively. What length below his eye can he see.of himself in the mirror?​

(A) 60cm
(B) 75cm
(C) 100cm
(D) 120cm

Answer 1

A) 60cm

Explanation:

From the given condition we can visualize the situation as shown in the schematic diagram.

We find that his eyes are situated at a distance of 30 cm above the lower edge of the mirror.

We now find that the last ray from the eye of the boy falling on the last reflecting elemental size mirror will also follow the law of reflection.

Therefore for the red rays as shown in figure using arrow the angle of incidence is equal to the angle of reflection.

• Then from the congruence triangles formed by the red rays and the normal to the mirror we find that he can see the images of his body 30 cm below the last point of the mirror.

Hence he can see a total of 60 cm of his vertical body length in the mirror.

TOPICS: reflection through a plane mirror, congruent triangles, alternate angles

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