Question

A plane-convex lens has a refractive index of 1.6 and a radius of curvature 60 cm. What is the focal length of the lens?

• A. 50 cm
• B. 100 cm
• C. 200 cm
• D. 150 cm

Answer 1

The correct option is B 100 cm

$R_1=60cm,R_2=\infty ,\mu =1.6$

$\frac{1}{f}=\left(\mu -1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

$\frac{1}{f}=\left(1.6-1\right)\left(\frac{1}{60}\right)$

$=f=100cm.$

Hence,

option $\left(B\right)$ is correct answer.