A) greater than 40 cm
B) equal to 40 cm
C) equal to 10 cm
D) less than 10 cm
Correct Answer: A
Solution :
When two lenses are separated by some distance \[x,\]then equivalent power \[P={{P}_{1}}+{{P}_{2}}-x\,{{P}_{1}}{{P}_{2}}\] \[\therefore \] \[P=5+5-x\times 5\times 5\] or \[P=10-25x\] Power P will be negative, if \[10-25x\]will be negative i.e., \[25x>10\] or \[x>\frac{10}{25}m\] or \[x>\frac{10}{25}\times 100\,cm\] or \[x>40\,cm\]
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