Q. A biconvex lens has radii of curvature, 20 cm each. If the refractive index of the material of the lens is 1.5, the power of the lens is :
A) Infinity
B) +2D
C) +20D
D) +5D
Explanation
[Solution] $\frac{1}{f} = (1.5-1)\left(\frac{1}{20} + \frac{1}{20}\right) = \frac{1}{20}$, so f = 20 cm and P = 100/20 = +5 D. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.