A) 24cm
B) 10cm
C) 15cm
D) 120cm
Correct Answer: D
Solution :
The focal length of the lens \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] \[\frac{1}{f}=(1.5-1)\left( \frac{1}{20}-\frac{1}{30} \right)\] \[\frac{1}{f}=0.5\left( \frac{30-20}{600} \right)\] Or \[\frac{1}{f}=\frac{1}{2}\times \frac{10}{600}=\frac{1}{120}\] or \[f=120\,cm\]You need to login to perform this action.
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