Question

A plano-convex lens is made of refractive index of $\mathrm{1.6.}$ The radius of curvature of the curved surface is $60cm$. The focal length of the lens is

• A. 400 cm
• B. 200 cm
• C. 100 cm
• D. 50 cm

Answer 1

Answer: (C)

Here, $\frac{1}{f}=(\mu -1)\left[\frac{1}{R_1}-\frac{1}{R_2}\right]$
$\frac{1}{f}=(1.6-1)\left[\frac{1}{60}-\frac{1}{\infty }\right]=\frac{1}{100}$
$\Rightarrow f=100cm$