The power P of a lens of focal length f (in metres) is given by
A{'text': 'P = c / f', 'label': 'A'}
B{'text': 'P = f / 100', 'label': 'B'}
C{'text': 'P = 1/f', 'label': 'C'}
D{'text': 'P = f²', 'label': 'D'}
Answer & Solution
Correct answer: C. {'text': 'P = 1/f', 'label': 'C'}
1. Power of a lens P = 1 / f (with f in metres).
2. Unit: dioptre (D). 1 D = 1 m⁻¹.
3. Convex lenses have P > 0, concave lenses P < 0.
_Source: NCERT Class 12 Physics Part II, Ch 9 §9.5.3_
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