Question

Radius of curvature of Plano-Convex lens is 10 cm and Focal length of lens is 30 cm. Then refractive index of material of lens is:-

• A. $1.65$
• B. $1.55$
• C. $1.33$
• D. $1.25$

Answer 1

Answer: (C)

$R_1=\infty R_2=-\mathrm{10}cm$

$\begin{array}{c}\text{We know,}\\ \frac{1}{f}=(n-1)(\frac{1}{R_1}-\frac{1}{R_2})\\ \Rightarrow \frac{1}{30}=(n-1)\left(\frac{1}{10}\right).\\ \Rightarrow n=4/3=1.333\end{array}$