Optics Question 688
Question: 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
[UPSEAT 2004]
Options:
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
Show Answer
Answer:
Correct Answer: B
Solution:
$ \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 _{l}=\frac{0.85}{-0.2} $
$ f _{a}=-4.25f _{a} $ .
