CBSE Class 10 Science 2017 · Paper 31/1/C · Question 8
Name the type of defect of vision a person is suffering from, if he uses convex lenses in his spectacles for the correction of his vision. If the power of the lenses is D, find the focal length of the lenses.
Answer
Hypermetropia (long-sightedness); the lens is convex, with m.
The person has hypermetropia (long-sightedness): nearby objects cannot be seen clearly because the near point of the eye is farther than cm, and a convex (converging) lens corrects it. (Presbyopia, in which the near point recedes with age, is also corrected with convex lenses for near vision.)
Focal length: m cm, a convex lens of focal length m.
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