Optics Question 589
Question: A glass convex lens $ ({\mu _{g}}=1.5) $ has a focal length of $ 8cm $ when placed in air. What would be the focal length of the lens when it is immersed in water ( $ {\mu _{w}}=1.33 $ )
[BHU 1994; MP PMT 1996]
Options:
A) 2 m
B) 4 cm
C) 16 cm
D) 32 cm
Show Answer
Answer:
Correct Answer: D
Solution:
$ \frac{f _{l}}{f _{a}}=\frac{{( _{a}}{\mu _{g}}-1)}{{( _{l}}{\mu _{g}}-1)} $
$ \frac{\sin 45^{o}}{\sin 30^{o}} $
$ \Rightarrow f _{w}=32cm $
