Question

The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of the cornea $\left(\right.7.8\, \, mm\left.\right)$ . 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.

• A. $4.0\,cm$
• B. $1\,cm$
• C. $2\,cm$
• D. $3.07\, cm$

Answer 1

Answer: (D)

We know eye lens is convex refracting surface.
Use expression for refraction from curved surface

$\mu _{1} \rightarrow $ Refractive index of medium having incident ray
$\mu _{2} \rightarrow $ Refractive index of a medium having reflected ray
$\frac{\mu _{2}}{v}-\frac{\mu _{1}}{u}=\frac{\mu _{2} - \mu _{1}}{R}$
$\frac{1.34}{v}-\frac{1}{\infty}=\frac{1.34 - 1}{7.8}$
$v=30.7 \, mm$
$v=3.07 \, cm$