A) 20 cm
B) 30 cm
C) 10 cm
D) 60 cm
E) 40 cm
Correct Answer: A
Solution :
From lens formula \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\] Giveh, \[v=\frac{u}{2},\]\[f=20\,cm\] \[\Rightarrow \] \[\frac{1}{20}=\frac{1}{u\text{/}2}-\frac{1}{u}=\frac{1}{u}\] \[\Rightarrow \] \[u=20\,cm\]You need to login to perform this action.
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