A doctor advises a patient to use spectacles with a convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. What is the power of the resultant combination:
A
-6.5 D
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B
-1.5 D
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C
6.5 D
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D
1.5 D
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Solution
The correct option is B -1.5 D P=P1+P2=140/100−125/100=2.5−4=−1.5D