Question

The far point of a myopic person is 40 cm. What should be the power of the lens that he must use to see clearly?

(a) -0.4 D

(b) +0.4 D

(c) -2.5 D

(d) +2.5 D

I had been asked this question during an interview for a job.

My doubt stems from Optical Instruments topic in portion Optics of Engineering Physics II

Answer 1

Correct choice is (c) -2.5 D

The best I can explain: Myopia is the defect when a person can’t see distant object clearly. To see clearly, the person should use a concave lens of focal length -40 cm.

Hence, the power of the lens = 100/-40

 = -2.5 Diopters.