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

Answer

A

Explanation

Converging power of cornea, `P_(c)=+40D`
Least converging power of eye lens, `P_(e)=+20D`
Power of the eye-lens, `P=P_(c)+P_(e)=40D+20D=60D`
Power of the eye lens
`P=(1)/("Focal length of the eye lens"(f))`
`f=(1)/(P)=(1)/(60D)=(1)/(60)m=(100)/(60)cm=(5)/(3)cm`
Distance between the retina and cornea - eye lens
= focal length of the eye lens `=(5)/(3)cm=1.67cm`