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. 200cm
• C. 100cm
• D. 400cm

Answer 1

The correct option is C 100cm

Radius of curvature of plane surface $R_1=\infty$

Radius of curvature of curved convex surface $R_2=-60cm$

Refractive index of material of lens $\mu =1.6$

Using lens maker formula : $\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})$

$\therefore$ $\frac{1}{f}=(1.6-1)(\frac{1}{\infty }-\frac{1}{-60})$

$⟹$ $f=100cm$