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JEE Main 2021 (16 Mar, Shift 2) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from JEE Main 2021 (16 Mar, Shift 2)

Q69JEE Main 2021 · 16 MAR · SHIFT 2Easy

Spherical Surfaces & Thin Lenses

The refractive index of a converging lens is 1.4. What will be the focal length of this lens if it is placed in a medium of same refractive index? Assume the radii of curvature of the faces of lens are R1 and R2 respectively.

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Answer: (b)

$\frac{1}{f} = \left(\frac{\mu_l}{\mu_m} - 1\right)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$
$\mu_m = \mu_l = 1.4 \Rightarrow \frac{1}{f} = 0$ , so $f = \infty$ .
So the answer is (b) Infinite.

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