Optics Question 701
Question: A thin equiconvex lens is made of glass of refractive index 1.5 and its focal length is 0.2 m, if it acts as a concave lens of 0.5 m focal length when dipped in a liquid, the refractive index of the liquid is
[EAMCET 2005]
Options:
A) $ \frac{17}{8} $
B) $ \frac{15}{8} $
C) $ \frac{13}{8} $
D) $ \frac{9}{8} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ \frac{f _{l}}{f _{a}}=\frac{ _{a}{\mu _{g}}-1}{ _{l}{\mu _{g}}-1} $
Therefore $ \frac{-0.5}{0.2}=\frac{1.5-1}{ _{l}{\mu _{g}}-1} $
Therefore $ _{l}{\mu _{g}}-1=-0.2 $
Therefore $ _{l}{\mu _{g}}=0.8=\frac{4}{5} $
Therefore $ \frac{ _{a}{\mu _{g}}}{ _{a}{\mu _{l}}}=\frac{4}{5} $
Therefore $ \frac{1.5}{ _{a}{\mu _{l}}}=\frac{4}{5} $
Therefore $ _{a}{\mu _{l}}=\frac{15}{8} $ .
