Q 12-09-194JEE MainJEE Main 2019 (10 Jan, Shift 2)Easy
The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of the cornea ($7.8\ \text{mm}$). This surface separates 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.
Answer: (D) $3.07\ \text{cm}$
Refraction at a spherical surface: $\dfrac{n_2}{v} - \dfrac{n_1}{u} = \dfrac{n_2-n_1}{R}$ with $u = \infty$:
$$\frac{1.34}{v} = \frac{0.34}{7.8\ \text{mm}} \;\Rightarrow\; v = \frac{1.34\times7.8}{0.34} \approx 30.7\ \text{mm} = 3.07\ \text{cm}$$
Solution by Sreeraj P, M.Sc Physics