Given:
Near point of the child = 10 cm
Far point of the child = 100 cm
The retina is at a distance of 2 cm behind the eye lens.
Thus, we have:
v = 2 cm = 0.02 m
When the near point is 10 cm,
u = − 10 cm = − 0.1 m
v = 2 cm = 0.02 m
The lens formula is given by
On putting the respective values, we get:
∴ Power of the lens, P = = 60 D
Now, consider the near point 100 cm.
Here,
u = − 100 cm = − 1 m
v = 2 cm = 0.02 m
The lens formula is given by
Putting the values, we get:
∴ Power of the lens = = 51 D
So, the range of the power of the eye lens is from + 60 D to + 51 D.