Question

The focal length of a plano-convex lens is equal to its radius of curvature. The value of the refractive index of its material is

• A. 1.33
• B. 1.6
• C. 1.5
• D. 2

Answer 1

The correct option is D 2

As per lens maker's formula

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

So as per given conditions we get u-1=1 which gives u=2