Q. Focal length of a converging lens in air is $R$. If it is dipped in water of refractive index 1.33, then its focal length will be around (Refractive index of lens material is 1.5)
A) $R$
B) $2R$
C) $4R$
D) $R/2$
Explanation
(c) $\frac{f_{l}}{f_{a}} = \frac{\ _{a}\mu_{g} - 1}{\ _{l}\mu_{g} - 1} \Rightarrow f_{l} = 4R$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.