alleryA lens has focal length 50 cm. Its power is:
A+2 D
B+0.5 D
C+5 D
D+50 D
Answer & Solution
Correct answer: A. +2 D
1. Convert focal length to metres: 50 cm = 0.5 m.
2. P = 1/f = 1/0.5 = +2.
3. The power is +2 dioptres (converging lens).
_Source: syllabus Science, Ch 9 "Light Reflection and Refraction", §9.4.4_
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