A) 50 cm
B) 100 cm
C) 200 cm
D) 400 cm
Correct Answer: B
Solution :
The focal length of a lens is given by \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] \[\left( \begin{align} & \text{where:}\,\text{R = }\infty \\ & {{R}_{2}}=-60\,cm \\ & \mu =1.6 \\ \end{align} \right)\] \[\frac{1}{f}=\left( 1.6-1 \right)\left( \frac{1}{\infty }=-\frac{1}{-60} \right)\] \[\frac{1}{f}=0.6\times \frac{1}{60}=\frac{1}{100}\] \[\Rightarrow \] \[f=100\,cm\]
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