Question

A doctor has prescribed a corrective lens of power -1.2Dto a person suffering from defect of vision .a)identify the defect from which he is suffering .b)find the focal length of the lens . please give answer in detail

Answer 1

a) The defect is Myopia. (It can be said by just seeing the negative sign in front of the prescribed power. )

Answer 2

(a) He is suffering from myopia

(b) Focal length, f = -83.4 cm

Explanation:

It is given that, doctor has prescribed a corrective lens of power (-1.2) D to a person suffering from defect of vision.

(a) Power, P = -1.2 D

Here, the power of the lens is negative. For a concave lens, the power is negative. Myopia is used to correct this defect. Power of a lens is reciprocal of focal length.

Power,

$P=\dfrac{1}{f}\\\\f=\dfrac{1}{D}\\\\f=\dfrac{1}{(-1.2\ D)}\\\\f=-83.4\ cm$

The focal length of a lens is (-83.4 cm).

Learn more,

Focal length

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