A) 12 cm
B) 60cm
C) 20cm
D) 30cm
Correct Answer: A
Solution :
Equivalent focal length \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] \[=\frac{1}{20}+\frac{1}{30}\] \[F=\frac{20\times 30}{20+30}=\frac{600}{60}=12\,\,cm\] \[F=12\,\,cm\]You need to login to perform this action.
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