The power of a convex lens of focal length 20 cm in dioptre unit is

0.5 0.05 5 2.5

5

The correct answer is Option (3) → 5 f = 20 cm = 0.2 m Power of lens is given by $P=\frac{1}{f}$ $P=\frac{1}{20 ~cm}=\frac{1}{20 \times 10^{-2}}$ dioptre ∴ P = 5D