A) -1.5D
B) -6.5D
C) + 6.5D
D) 4- 6.67 D
Correct Answer: A
Solution :
Focal length of combination can be calculated as \[\frac{1}{f}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\] \[\Rightarrow \] \[\frac{1}{F}=\frac{1}{40}+\frac{1}{(-25)}\] \[\Rightarrow \] \[\frac{1}{F}=\frac{-200}{3}cm\] \[=\frac{100}{-200/3}\] = 1.5 DYou need to login to perform this action.
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