alleryA concave lens has a focal length of -25 cm. Its power is:
A+4 D
B-4 D
C-0.25 D
D+0.25 D
Answer & Solution
Correct answer: B. -4 D
1. f = -25 cm = -0.25 m.
2. P = 1/f = 1/(-0.25) = -4.
3. Power is -4 D, consistent with a diverging concave lens.
_Source: syllabus Science, Ch 9 "Light Reflection and Refraction", §9.4.4_
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