Optics Question 615
Question: A convex lens of focal length 12 cm is made of glass of $ \mu =\frac{3}{2} $ . What will be its focal length when immersed in liquid of $ \mu =\frac{5}{4} $
[MP PMT 1995, 2003]
Options:
A) 6 cm
B) 12 cm
C) 24 cm
D) 30 cm
Show Answer
Answer:
Correct Answer: A
Solution:
$ \frac{f _{l}}{f _{a}}=\frac{{( _{a}}{\mu _{g}}-1)}{{( _{l}}{\mu _{g}}-1)}= $ $ \frac{( \frac{3}{2}-1 )}{( \frac{3/2}{5/4}-1 )}=\frac{5}{2} $
$ \therefore $ $ f _{l}=f _{a}( \frac{5}{2} )=\frac{12\times 5}{2}=30 $ $ cm $
