A) 15 cm
B) -15 cm
C) -30 cm
D) 30 cm
Correct Answer: C
Solution :
Using the relation for combined focal length \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}=\frac{1}{60}+\frac{1}{(-20)}\] (Here: \[{{f}_{1}}=60\,cm\,{{f}_{2}}=-20\,cm\]) \[\frac{1}{f}=\frac{1}{60}-\frac{1}{20}=\frac{1-3}{60}=\frac{-2}{60}\] \[f=-30\,cm\]You need to login to perform this action.
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