Question

The uncorrected eye. For the following questions, assume that the distance between the eye lens and the retina is 1.70 cm. In other words, since the image is always formed on the retina, the distance between the lens and the image is always 1.70 cm. Also note that, as is seen in the ray diagram, since the eye lens is converging and the image is on the opposite side of the lens compared to the object, the image is always real.

One farsighted patient has a near point of 40.0 cm. What is the focal length of his eye when an object is at his near point?

Answer 1

Farsighted patient is that who is not able to saw the objects that are nearby to his eye as the image formed is behind the retina and hence he can only visualise the objects which are farther because for far away object the image formed is on retina.

Now for focal lengh

Here in our question:- image distance =1.70cm=0.017m

Object distance=-40cm= -0.40m

Substitution of values in the formula we get:-

f=0.017754569 m