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} $ .



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