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A convex lens of focal length 25 cm has power equal to:
A+1 D
B+2 D
C+4 D
D+25 D
Answer & Solution
Correct answer: C. +4 D
1. P = 1 / f, with f in METRES.
2. f = 25 cm = 0.25 m.
3. P = 1 / 0.25 = +4 D.
_Source: NCERT Class 10 Science Ch 9 §9.3.6 Power Calculation_
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