Q. A bi-convex lens made of glass (refractive index 1.5) is put in a liquid of refractive index 1.7. Its focal length will
A) Decrease and change sign
B) Increase and change sign
C) Decrease and remain of the same sign
D) Increase and remain of the same sign
Explanation
(b) $\frac{f_{l}}{f_{a}} = \frac{\ _{a}\mu_{g} - 1}{\ _{l}\mu_{g} - 1} = \frac{(1.5 - 1) \times 1.7}{(1.5 - 1.7)}$
$\Rightarrow f_{1} = \frac{0.85}{- 0.2}f_{a} = - 4.25\ f_{a}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.