A person has been using spectacles of power -1.0 diopter for distant vision and a separate reading glass of power 2.0 diopters. What is the least distance of distinct vision for this person?
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A person has been using spectacles of power −1.0 diopter for distant vision and a separate reading glass of power 2.0 diopters. What is the least distance of distinct vision for this person?

G1 Physics · Accepted Answer

For the reading lens, f = 1/P = 0.5 m = 50 cm. Taking the object at 25 cm, lens formula gives 1/v − 1/(−25) = 1/50. Hence 1/v = −1/50, so v = −50 cm. Therefore the person's least distance of distinct vision is 50 cm.