A) 0.20 m
B) -0.60 m
C) 0.30 m
D) 0.40 m
Correct Answer: B
Solution :
From lens formula \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{\sqrt{{{R}_{2}}}} \right)\] where \[{{R}_{1}},{{R}_{2}}\] are radii of curvatures and \[\mu \]the refractive index. Given, \[R=-20\,cm\], \[{{R}_{2}}=\infty \] (plano-convex lens), \[\mu =\frac{4}{3}\] \[\frac{1}{f}=\left( \frac{4}{3}-1 \right)\left( \frac{1}{-20}-\frac{1}{\infty } \right)\] \[\Rightarrow \] \[\frac{1}{f}=\frac{1}{3}\times \left( \frac{1}{-20} \right)\] \[\Rightarrow \] \[f=-60\,\,cm=-0.6\,m\]You need to login to perform this action.
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