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JEE Main 2019 (10 Apr, Shift 1) · Combination of Lenses

Combination of Lenses question from JEE Main 2019 (10 Apr, Shift 1)

Q58JEE Main 2019 · 10 APR · SHIFT 1Medium

Combination of Lenses

One plano-convex and one plano-concave lens of same radius of curvature 'R' but of different materials are joined side by side as shown in the figure. If the refractive index of the material of 1 is $\mu$ 1 and that of 2 is $\mu$ 2, then the focal length of the combination is:

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Answer: (c)

Lens 1 plano-convex: $\frac{\mu_1-1}{R}$ ; lens 2 plano-concave: $-\frac{\mu_2-1}{R}$ .
$\frac{1}{f} = \frac{\mu_1-\mu_2}{R}$
So the answer is (c) $\frac{R}{\mu_1-\mu_2}$ .

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