Q. One surface of a lens is convex and the other is concave. If the radii of curvature are $r_{1}\ and\ r_{2}$ respectively, the lens will be convex, if
A) $r_{1} > r_{2}$
B) $r_{1} = r_{2}$
C) $r_{1} < r_{2}$
D) $r_{1} = 1/r_{2}$
Explanation
(c) $\frac{1}{f} = (\mu - 1)\left( \frac{1}{r_{1}} - \frac{1}{r_{2}} \right)$
For lens to be concave, $\left( \frac{1}{r_{1}} - \frac{1}{r_{2}} \right) > 0$
Or $\frac{1}{r_{1}} > \frac{1}{r_{2}}\ $or$\ {\ r}_{1} < r_{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.