Question

A plano-convex lens is made of material of refractive index $1.6$. The radius of curvature of the curved surface is $60cm$. The focal length of the lens is :

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

Answer 1

The correct option is B $100cm$

Given,

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

From lens makers formula, $\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$

$\frac{1}{f}=(1.6-1)\left(\frac{1}{60}\right)\Rightarrow f=100cm.$