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A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for the:i. defect of visionii. for its correction
A student cannot see a chart hanging on a wall placed at a distance of 3 m (or, 300 cm) from him, it means the student is suffering from 'myopia' or short-sightedness. Since, in myopia, a person can see nearby objects, but not distant objects, clearly as the far point of the eye is closer to him than normal. It can be corrected by using a concave lens of suitable power.
The ray diagram to illustrate the defect and the correction are as follows:
i. defect of vision:
ii. for its correction:
Explanation:
Myopia, also known as near-sightedness or short-sightedness, is a defect of vision in which a person can't see the distant object clearly (appears blurred), though can see the nearby objects clearly. The far point of a myopic eye is less than infinity.
This defect occurs either due to the high converging power of the eye lens, (because of its short focal length). Or, due to the eye-ball being too long, which causes light to focus in front of the retina, instead of directly on the retina.
It is corrected by using spectacles containing concave lenses, which should be of such a focal length (or power) that it produces a virtual image of the distant object (lying at infinity) at the far point of the myopic eye.
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