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. 2
• B. 1.5
• C. 1.6
• D. 1.33

Answer 1

Answer: (A)

2

Answer 2

Using $\frac{1}{f}=(n-1) \left( \frac{1}{R_1}+\frac{1}{R_2}\right)$ we get
$\frac{1}{f}=(n-1) \frac{1}{f} i.e., n=1 +1 =2$