A) \[20\,\,cm\]
B) \[60\,\,cm\]
C) \[40\,\,cm\]
D) \[30\,\,cm\]
Correct Answer: C
Solution :
Focal length of the plano-convex lens is \[\frac{1}{f}=({{\mu }_{g}}-1)\left( \frac{1}{20}-\frac{1}{\infty } \right)\] \[=\left( \frac{3}{2}-1 \right)\left( \frac{1}{20} \right)=\frac{1}{2}\times \frac{1}{20}\] \[\Rightarrow \] \[f=40\,\,cm\] If point object \[O\] is placed at a distance of \[40\,\,cm\] from the plano-convex lens, rays become parallel and final image is formed at second focus or \[40\,\,cm\] from concave lens which is independent of\[a\].You need to login to perform this action.
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