A) 15 cm
B) -15 cm
C) - 30 cm
D) 30 cm
Correct Answer: C
Solution :
The focal length (f) of the combination of concave and convex lens is \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] where \[{{f}_{1}}=+60\,cm\], \[{{f}_{2}}=-20\,\,cm\] \[\therefore \] \[\frac{1}{f}=\frac{1}{60}-\frac{1}{20}\] \[\Rightarrow \] \[\frac{1}{f}=\frac{-2}{60}\] \[\Rightarrow \] \[f=-30\,\,cm\]You need to login to perform this action.
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