A) 3.0
B) 2.0
C) 2.5
D) 1.5
Correct Answer: D
Solution :
Here \[\frac{1}{F}=\frac{2}{f}+\frac{1}{{{f}_{m}}}\] Plano-convex lens silvered on plane side has \[{{f}_{m}}=\infty \]. \[\therefore \] \[\frac{1}{F}=\frac{2}{f}+\frac{1}{\infty }\Rightarrow \frac{1}{30}=\frac{2}{f}\Rightarrow f=60\,\,cm\] Plano-convex lens silvered on convex side has \[{{f}_{m}}=\frac{R}{2}\] \[\therefore \]\[\frac{1}{F}=\frac{2}{f}+\frac{2}{R}\Rightarrow \frac{1}{10}=\frac{2}{60}+\frac{2}{R}\Rightarrow R=30\,cm\] Now using \[\frac{1}{f}=(\mu -1)\left( \frac{1}{R} \right)\], we get \[\mu =1.5\]
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