JEE Main · 2024 · 06 Apr 2024 · Shift 2 · Geometrical Optics

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

(A)1.8
(B)1.4
(C)1.5✓ Correct
(D)1.2

Answer: (C)

Solution

By the lensmaker's equation,

\frac{1}{f} = (μ - 1) (\frac{1}{R _{1}} - \frac{1}{R _{2}})

. With

R_{1} = 15

cm,

R_{2} = - 30

cm and

f = 20

cm:

\frac{1}{20} = (μ - 1) (\frac{1}{15} + \frac{1}{30}) = (μ - 1) \cdot \frac{1}{10}

μ - 1 = 0.5

μ = 1.5

JEE Main · 2024 · 06 Apr 2024 · Shift 2 · Single correct option

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