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JEE Main 2019 (10 Jan, Shift 2) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from JEE Main 2019 (10 Jan, Shift 2)

Q89JEE Main 2019 · 10 JAN · SHIFT 2Medium

Spherical Surfaces & Thin Lenses

The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of cornea (7.8 mm). This surface separateds two media of refractive indices 1 and 1.34. Calculate the distance from the refracting surface at which a parallel beam of light will come to focus -

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Answer: (b)

For a parallel beam ( $u = \infty$ ): $\frac{\mu_2}{f} = \frac{\mu_2 - \mu_1}{R}$ .
$f = \frac{\mu_2 R}{\mu_2 - 1} = \frac{1.34 \times 7.8}{0.34}$ mm
$f \approx 30.7$ mm $\approx 3.1$ cm
So the answer is (b) 3.1 cm.

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