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प्रश्न
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
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उत्तर
Hypermetropia is a defect of vision because of which a person cannot see nearby objects clearly but has normal distant vision. Hypermetropia occurs because the converging power of the eye lens is low and the images of nearby objects are formed behind the retina. As a result, the person cannot see these objects clearly. In certain other cases, hypermetropia is caused because the eye ball is too short. This, too, causes the formation of images behind the retina, as the retina is at a smaller distance from the eye lens. The near point of a hypermetropic eye is located more than 25 centimetres from the eye. The following ray diagram explains the hypermetropic eye and how the defect is corrected by using convex lenses. A convex lens is a converging lens that converges light rays and forms virtual images of nearby objects at the eye's near point. The eye lens then easily focusses the light rays from the near point and forms clear images of the objects on the retina.
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| Column - I | Column - II |
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| 2. Pupil | b. Far point comes closer |
| 3. Ciliary muscles | c. near point moves away |
| 4. Myopia | d. Screen of the eye |
| 5. Hypermetropia | e. Power of accommodation |
