Q. The focal length of a convex lens is $10\ cm$ and its refractive index is 1.5. If the radius of curvature of one surface is 7.5 $cm$, the radius of curvature of the second surface will be
A) $7.5\ cm$
B) $15.0\ cm$
C) $75\ cm$
D) $5.0\ cm$
Explanation
(b) $\frac{1}{f} = (\mu - 1)\left( \frac{1}{R_{1}} - \frac{1}{R_{2}} \right)$
$\Rightarrow \frac{1}{+ 10} = (1.5 - 1)\left( \frac{1}{+ 7.5} - \frac{1}{R_{2}} \right) \Rightarrow R_{2} = - 15\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.