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Question
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
Options
+ 0.5 D
– 0.5 D
+ 0.2 D
– 0.2 D
Solution
– 0.5 D
Explanation -
The person is suffering from myopia. He needs a concave lens and hence power would be negative.
Object distance, u = - ∞
Image distance, υ = -2 m
Using lens formula
`1/upsilon - 1/"u" = 1/"f"`
`1/f = 1/(-2) - 1/∞`
f = -2 m
`P = 1/f = -1/(2 "m") = -0.5 "D"`
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