A person cannot see distinctly objects kept beyond 2m.This defect can be corrected by using a lens of what power?

The eye defect in which a person cannot see objects beyond near point or far objects but can see the near objects clearly is called Myopia. This defect can be corrected by using biconvex lens.

Given distance of far point (D) = 2m

Let f be the focal length of eye lens.

Image distance (distance between eye lens and retina) for our human eye is always constant and is about 2.5 cm.

This is due to the action of ciliary muscles.

applying lens formula, we get

f = -D

= -2 cm.

but , the power of a lens is reciprocal of focal length.

hence. Power = 1/f. (f in meters)

= 1/-2

= – 0.5 dioptre.

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