Q. A plano-concave lens is made up of glass of refractive index 1.5 and the radius of the curvature of its curved face is 100 cm. What is the power of the lens?
A) $+ \ 0.5\ D$
B) $- 0.5\ D$
C) $- 2\ D$
D) $+ 2\ D$
Explanation
(b) $P = \frac{1}{f} = (\mu - 1)\left( \frac{1}{R_{1}} - \frac{1}{R_{2}} \right)$
$= (1.5 - 1)\left( \frac{1}{\infty} - \frac{1}{1} \right)$
$= 0.5( - 1)$
$P = \ - 0.5\ D$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.