Ray Optics Question 6
Question 6 - 2024 (29 Jan Shift 1)
A biconvex lens of refractive index 1.5 has a focal length of $20 cm$ in air. Its focal length when immersed in a liquid of refractive index 1.6 will be:
(1) $-16 cm$
(2) $-160 cm$
(3) $+160 cm$
(4) $+16 cm$
Show Answer
Answer: (2)
Solution:
$\mu _1=1.5$
$\mu _m=1.6$
$f _a=20 cm$
As $\frac{f _m}{f _a}=\frac{\left(\mu _1-1\right) \mu _m}{\left(\mu _1-\mu _m\right)}$
$\frac{f _m}{20}=\frac{(1.5-1) 1.6}{(1.5-1.6)}$
$f _m=-160 cm$
