Question:
A person needs a lens of power -4.5 D for correction of her vision.
(a) What kind of defect is she suffering from ?
(b) What is the focal length of the corrective lens ?
(c) What is the nature of the corrective lens ?
(CBSE Sample Paper 2017-18)
Solution:
(a) She is suffering from myopia
(b) $f=\frac{1}{\mathrm{P}}=-\frac{1}{4.5}=-0.22 \mathrm{~m}=-22 \mathrm{~cm}$
(c) Concave lens.
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