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Power of a lens of focal length f (in metres) is given by:
AP = 1 / f
BP = f / 1
CP = f · f
DP = 2 / f
Answer & Solution
Correct answer: A. P = 1 / f
1. Power P = 1 / f, with f in metres.
2. SI unit of power is the dioptre (D = m⁻¹).
3. Convex (converging) lens: P positive. Concave (diverging): P negative.
_Source: NCERT Class 10 Science Ch 9 §9.3.6 Power of a Lens_
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