alleryA hypermetropic person has a near point of 1 m. The focal length of the corrective convex lens is:
A+25 cm
B+100 cm
C-33.3 cm
D+33.3 cm
Answer & Solution
Correct answer: D. +33.3 cm
1. The corrective lens must form the image of 25 cm (normal near point) at the person's near point (100 cm).
2. Using 1/v - 1/u = 1/f with u = -25 cm and v = -100 cm: 1/f = -1/100 + 1/25 = 3/100.
3. Hence f = +33.3 cm (≈ +3 D).
_Source: syllabus Science, Ch 10 "The Human Eye and the Colourful World", §10.2_
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