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Q18
(CISF/2019)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
The minimum length of a plane mirror to see your full length image is
Explanation
To see a full-length image in a plane mirror, the minimum length of the mirror must be half of the height of the person. This is a standard application of the laws of reflection and geometry.
- To see the top of the head, light rays from the head must reflect off the mirror and enter the eyes. The required reflection point is halfway between the eye level and the top of the head.
- To see the feet, light rays from the feet must reflect off the mirror and enter the eyes. The required reflection point is halfway between the eye level and the feet.
The total length of the mirror required is the distance between these two points, which equals (1/2 × height above eyes) + (1/2 × height below eyes) = 1/2 × total height. This requirement is independent of the distance between the person and the mirror, provided the mirror is placed at the correct vertical position.
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