A) \[\frac{R}{2}\]
B) R
C) 2R
D) \[1.5R\]
Correct Answer: C
Solution :
For a lens, \[\frac{1}{f}=(\mu -1)\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] For plano-convex lens, \[{{R}_{2}}\] (say) \[=\infty ,\mu =1.5,\] \[\frac{1}{f}=\frac{(1.5-1)\times 1}{R}=\frac{0.5}{R}=\frac{1}{2R}\] \[\Rightarrow \] \[f=2R\]
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