Question

The power of a biconvex lens is 10 dioptre and the radius of curvature of each surface is 10 cm. Then the refractive index of the material of the lens is :

• A. $\frac{3}{2}$
• B. $\frac{4}{3}$
• C. $\frac{9}{8}$
• D. $\frac{5}{3}$

Answer 1

Answer: (A)

$\frac{3}{2}$

$P=\frac{1}{f}\Rightarrow f=\frac{1}{P}f=\frac{1}{10}m=\frac{100cm}{10}=10cm$

Now

$\frac{1}{f}=(\mu -1)(\frac{1}{R_1}-\frac{1}{R_2})=\frac{1}{10}=(\mu -1)(\frac{1}{10}-(-\frac{1}{10}\left)\right)\Rightarrow \frac{1}{10}=(\mu -1)\frac{2}{10}\Rightarrow \mu -1=\frac{1}{2}\Rightarrow \mu =1+\frac{1}{2}=\frac{3}{2}$