Question

Prove that the power of accommodation of a normal human eye is 4D.

Answer 1

vision length 25 cm
focal length f=0.25m
power=1/f =1/0.25
=100/25=4D

Answer 2

HI !

The minimum distance needed to see objects clearly is called the near point.
For humans,the near point is 25 cm ( 25/100 m)

Hence,

Focal length = f = 25/100 m

Power = 1/f
           = 1/(25/100)
           = 100/25
           = 4 D

Proved.