Question

A double convex lens has radii of curvature of 1 m and 2m, What should be the refractive index of the material such that the focal length of the lens is 50 cm?

• A. $3\frac{1}{3}$
• B. $2\frac{1}{3}$
• C. $4\frac{1}{3}$
• D. $1.13$

Answer 1

The correct option is D $1.13$

Given,

$R_1=1m=10cm$

$R_2=2m=20cm$

$f=50cm$

$n=?$

Using the lens makers formula:

$\frac{1}{f}=(n-1)(\frac{1}{R_1)}-\frac{1}{R_2}$

$\frac{1}{50}=(n-1)(\frac{1}{10}+\frac{1}{20})$

Solving the above equation we get,

Refractive index, $n=1.13$