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.

part e) The nearsighted patient in part c tries to view an object that is very far away (object at infinity). Use the focal length calculated in part c to determine the location of the image. How does this compare to the distance from the eye lens to the retina? What kind of image is seen on the retina?

part f) The farsighted patient in part d tries to view an object that is 25cm away, which a person with normal vision can see clearly. Use the focal length calculated in part d to determine the location of the image. How does this compare to the distance from the eye lens to the retina? What kind of image is seen on the retina?

calculated pt c: f= 1.70cm calculated pt d: f= 1.63cm

Answer 1

Here I will use a convention that the distance measured in the direction incident light (i.e. coming from object) will be +Ve and in the opposite direction will be negative. If the image distance, what you will obtain, is positive then the image will be real.

part (e) object is in the infinity and the image will form at the focal plane. From the lens equation you can find the image distance (v)

Therefore, the image will form on the retina for far distant objects. The image is on the opposite side of the lens compared to the object, the image is always real.

Part (f) From the lens equation you can obtain the image distance. the focal length of the eye lens is f = 1.70 cm (conversing time) and the object distance (u) = -25 cm. Therefore, from the lens equation, you can obtain

The image will be formed at a distance 1.74 cm behind the eye lens. The image will be real and it will form behind the retina as the retina is in potion of 1.63 cm away.