A) 10.5
B) 12.0
C) 13.5
D) 15.5
Correct Answer: C
Solution :
\[d=\frac{2f}{3}\] or \[f=\frac{3d}{2}=\frac{3\times 12}{2}=18cm\] Equivalent focal length is \[f=\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}=\frac{18\times 18}{18+18}+\frac{18}{4}\] \[=9+4.5\] \[=13.5\,\,cm\]You need to login to perform this action.
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