Question

A biconvex lens of a focal length of 10 cm is to be made from a glass material. If the refractive index of the material is 1.5, what must be the radius of curvature of the surface of the lens?

a) 0.1 m

b) 0.15 m

c) 0.20 m

d) 0.30 m

Answer 1

Step 1, Given data

Focal length f = 10 cm

Refractive index = 1.5

Step 2, Finding the radius of curvature

From the lens maker formula

We know,

$\frac{1}{f}=(\mu -1)[\frac{1}{R_1}-\frac{1}{R_2}]$

Since the given lens is a biconvex lens So $R_1=R_2=R$

Putting all the values

$\frac{1}{10}=(1.5-1)[\frac{1}{R}+\frac{1}{R}]$

After solving

R = 10 cm = 0.1 m

Hence the radius of curvature of the lens will be 0.1 m