An eye specialist prescribes spectacles having a combination of convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in diopter is
A
+1.5
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B
−1.5
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C
+6.67
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D
−6.67
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Solution
The correct option is B−1.5 Power of combination = P1+P2 =1f1+1f2{∵P=1f} =10.4−10.25 =2.5−4=−1.5 D