Question

A person, whose eye has a lens-to-retina distance of 2.0 cm, can only clearly see objects that are closer than 1.0 m away. what is the strength

Answer 1

To calculate the strength of the eye lens, we use the formula

$\frac{P}{100} = \frac{1}{f} =\frac{1}{u} +\frac{1}{v}$  ( thin lens formula)

Here, u is the object distance and v is image distance.

Given, $u =1 m=100cm$ and $v = 2 cm$

Therefore,

$\frac{1}{f} =\frac{1}{100} + \frac{1}{2}$

$\frac{1}{f} = 0.01 + 0.5$$= 0.51 cm$

Thus, strength of the eye lens is

$P= \frac{100}{f} =\frac{100}{\frac{1}{0.51} } = 51 D$