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A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be:
A
concave, –0.2 diopter
B
convex, +0.15 diopter
C
convex, +2.25 diopter
D
concave, –0.25 diopter
Explanation
Concave lens with f equal to the far point distance.
Detailed Solution
To correct myopia, the far point must go to infinity: v = –4 m, u = –∞.
$P = \frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{-4} - \frac{1}{-\infty} = -0.25$ D
The negative sign implies a concave lens.
$P = \frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{-4} - \frac{1}{-\infty} = -0.25$ D
The negative sign implies a concave lens.