A) 10 cm
B) 12 cm
C) 15 cm
D) 18 cm
Correct Answer: B
Solution :
By using the lens equation, \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\] \[\frac{1}{20}+\frac{1}{30}=\frac{1}{f}\Rightarrow \frac{1}{f}=\frac{1}{20}+\frac{1}{30}\] \[\Rightarrow \frac{1}{f}=\frac{3+2}{60}=\frac{5}{60}\Rightarrow f=12\,cm\]You need to login to perform this action.
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