Optics Question 650
Question: A lens which has focal length of 4 cm and refractive index of 1.4 is immersed in a liquid of refractive index 1.6, then the focal length will be
[RPMT 1999]
Options:
A) - 12.8 cm
B) 32 cm
C) 12.8 cm
D) - 32 cm
Show Answer
Answer:
Correct Answer: A
Solution:
$ \frac{f _{l}}{f _{a}}=( \frac{ _{a}{\mu _{g}}-1}{ _{l}{\mu _{g}}-1} )\Rightarrow \frac{f _{l}}{4}=\frac{(1.4-1)}{\frac{1.4}{1.6}-1}\Rightarrow f _{l}=-12.8cm $
