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The power P of a lens with focal length f (in metres) is:
AP = f (in m)
BP = 1/f, in diopters (D), where 1 D = 1 m⁻¹
CP = f² (in m²)
DP = 100/f (in D when f in cm)
Answer & Solution
Correct answer: B. P = 1/f, in diopters (D), where 1 D = 1 m⁻¹
**Power P = 1/f** in **diopters (D)**, with f in **metres**. A converging lens has positive P; diverging lens has negative P. Higher |P| → stronger lens (shorter focal length). E.g., f = 0.5 m → P = +2 D.
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