For the thin convex lens, the radii of curvature are at 15 cm and 30 cm respectively. The focal length of the lens is 20 cm. The refractive index of the material is: (a) 1.2 (b) 1.5 (c) 1.4 (d) 1.8

Answer: (b). 1/f = (μ - 1)(1/15 + 1/30) = (μ - 1)/(10) 1/20 = (μ - 1)/(10) ⇒ μ - 1 = 0.5 So the answer is (b) 1.5.

For the thin convex lens, the radii of curvature are at 15 cm and 30… | JEE Main 2024 (6 Apr, Shift 2)

Q38JEE Main 2024 · 6 APR · SHIFT 2Easy

Spherical Surfaces & Thin Lenses

For the thin convex lens, the radii of curvature are at $15\text{ cm}$ and $30\text{ cm}$ respectively. The focal length of the lens is $20\text{ cm}$ . The refractive index of the material is:

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Answer: (b)

$\frac{1}{f} = (\mu - 1)\left(\frac{1}{15} + \frac{1}{30}\right) = \frac{\mu - 1}{10}$
$\frac{1}{20} = \frac{\mu - 1}{10} \Rightarrow \mu - 1 = 0.5$
So the answer is (b) 1.5.

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