For a normal eye, the cornea of eye provides a converging power of `40 D` and the least converging power of the eye lens behind the cornea is `20 D`. Using this information, the distance between the retina and the cornea eye lens can be estimated to be

Options

A. 5 cm
B. 2.5 cm
C. 1.67 cm
D. 1.5 cm

Answer

C

Explanation

Given, power `(P_(1)) = 40 D` and power `(P_(2))=20 D`
We have,
`P_("eq")=P_(1)+P_(2)=40+20=60 D`
So, `" "(1)/(f_("eq"))=(1)/(f_(1))+(1)/(f_(2))`
`rArr " " f_("eq")=(100)/(P_("eq"))=(100)/(60)`
`= 1.67 cm`