A) Convergent lens of focal length 3.5 R
B) Convergent lens of focal length 3.0 R
C) Divergent lens of focal length 3.5 R
D) Divergent lens of focal length 3.0 R
Correct Answer: A
Solution :
\[\frac{{{f}_{l}}}{{{f}_{a}}}=\frac{_{a}{{\mu }_{g}}-1}{_{l}{{\mu }_{g}}-1}=\frac{1.5-1}{\frac{1.5}{1.75}-1}\]= \[-\frac{1.75\times 0.50}{0.25}=-3.5\] \[\therefore {{f}_{l}}=-\,3.5\ {{f}_{a}}\,\Rightarrow \,{{f}_{l}}=+\,3.5\,R\] (Q fa = R) Hence on immersing the lens in the liquid, it behaves as a converging lens of focal length 3.5 R.
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