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Question
Solve the following question:
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
Solution
Since the near point of the eye is 50 cm which is greater than 25 cm, a person is suffering from hypermetropia.
Object distance (u) = - 25cm
Image distance (v) = - 50cm
Using lens formula
`1/"f" = 1/"v" - 1/"u"`
`1/"f" = 1/(-50) - 1/(-25)`
`1/"f" = -1/50 + 1/25`
`1/"f" = (-1+2)/50`
`1/"f" = 1/50`
`"f"` = +50 cm
Since the focal length of the lens is positive, corrective lens required is convex lens.
`"f"` = +50cm
`"f"` = +0.5m
Power (P) of corrective lens will be
`"P" = 1/("f"("m"))`
`"P" = 1/0.5`
`"P" = + 2 "D"`
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