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

Answer

C

Explanation

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