Q. 19

# A normal eye has retina 2 cm behind the eye-lens when the eye is (A) fully relaxed, (B) most strained?

Answer :

(a)When the eye lens is fully relaxed , *u = ∞*

The retina is 2 cm behind the eye-lens,hence *v* = 2 cm = 0.02 m

Using lens formula –

Substituting the values-

Hence, the power of the eye lens is

So, when the eyes are fully relaxed condition, eye lens has a power of 50 D

(b)When the eye lens is strained-

Distance of object *u* = – 25 cm = – 0.25 m

Using lens formula –

Substituting the values-

Hence, power of the eye lens becomes-

So, when the eyes are most strained condition, eye lens has a power of 54 D.

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