Refractive index of a glass convex lens is 1.5. The radius of curvature of each of the two surfaces of the lens is 20 cm. The ratio of the power of the lens when immersed in a liquid of refractive index 1.25 to that when placed in air is (a) 2: 3 (b) 2: 5 (c) 3: 5 (d) 5: 2

Answer: (b). (Pl)/(Pa) = ((μ)/(μl) - 1)/(μ - 1) (radius does not matter). (1.5)/(1.25) - 1 = 0.2, so (Pl)/(Pa) = (0.2)/(0.5) = 2/5 So the answer is (b) 2: 5.

Refractive index of a glass convex lens is 1.5. The radius of… | MHT CET 2023 (14 May, Shift 2)

Q57MHT CET 2023 · 14 MAY · SHIFT 2Medium

Spherical Surfaces & Thin Lenses

Refractive index of a glass convex lens is 1.5. The radius of curvature of each of the two surfaces of the lens is $20\text{ cm}$ . The ratio of the power of the lens when immersed in a liquid of refractive index 1.25 to that when placed in air is

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Answer: (b)

$\frac{P_l}{P_a} = \frac{\frac{\mu}{\mu_l} - 1}{\mu - 1}$ (radius does not matter).
$\frac{1.5}{1.25} - 1 = 0.2$ , so $\frac{P_l}{P_a} = \frac{0.2}{0.5} = \frac{2}{5}$
So the answer is (b) $2 : 5$ .

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