Lab 11_ The Human Eye

Temple University College of Science and Technology Physics Department Physics 1022 Section 052 Lab 11 The Human Eye

Lab 11: The Human Eye 11/16/2023 Group Members Cynthia Klingensmith, Helen Luong Goals The goal of this lab is to further our understanding of lenses and refraction. We will observe how the human eye functions and how corrective lenses are used to fix problems related to vision. We will look at how images are translated and formed on the retina of the eye and how it focuses and accommodates objects at differing distances. Additionally, we will observe vision issues such as near and far-sightedness and learn how they can be corrected. Procedure Part 1: - Before beginning the experiment, draw a diagram of the human eye represented by each part of the model. - Compare the image location for an eye filled with air to an eye filled with water. Put the +62 mm lens in Slot A near the cornea. Place the Pasco Basic Optics Light Source about 30 cm from the cornea of the eye model. The cross target on the front of the light source will be the subject. - Take the white plastic retina screen and try to locate a position inside the eye model where a sharp image of the cross target is formed and record the image distance. - Make a prediction assuming that, as in the real human eye, the lens is about the same index of refraction as water: Will adding water to the eye model increase or decrease the refraction angle? Will this increase or decrease the image distance, with all other things being equal? - Fill the eye model with water to 1 or 2 cm of the top. Now see if you locate the retina screen at a position where the cross-target image is formed and record the value. Part 2:

Part 2 With the 62 mm lens in slot A and a NORMAL retina screen: - NORMAL Slot Distance: 32 cm or 320 mm - Image distance: 52 cm or 520 mm - Focal length: 1 / f = 1 / d ₀ + 1 / dᵢ 1 / f = 1 / 520 + 1 / 320 f = 4160 / 21 f = 198 mm Mimicking farsighted eyesight by moving the retina screen to FAR slot: - FAR Slot distance: 92 cm or 920 mm - Image distance: 112 cm or 1120 mm - Focal length 1 / f = 1 / d ₀ + 1 / dᵢ 1 / f = 1 / 1120 + 1 / 920 f = 25760 / 51 f = 505 mm Mimicking nearsighted eyesight by moving the retina screen to the NEAR slot:

- NEAR Slot Distance: 26 cm or 260 mm - Image distance: 46 cm or 460 mm - Focal length: 1 / f = 1 / d ₀ + 1 / dᵢ 1 / f = 1 / 460 + 1 / 260 f = 1495 / 9 f = 166.1 mm Which type of lens will help correct farsighted vision so that it can see as well as the normal eye: - Prediction: A converging lens will help correct the farsighted eye. Questions 1. Notice that the lenses have their focal lengths stamped onto the handle, why are some of the values positive and some negative? This distinction reflects the correction needed for different vision problems. Nearsighted individuals have difficulty seeing distant objects clearly, while they can see nearby objects well. On the other hand, farsighted individuals can see distant objects without issue but struggle with seeing things up close. To correct farsightedness, a converging lens with a positive focal length is used. Conversely, nearsightedness is corrected using a diverging lens, which is indicated by a negative focal length. 2. Is the image on the retina a real or virtual image? Explain. Yes, the image that forms on the retina of the eye is real because it is not reflected off of anything. 3. Was your prediction above proven correct or incorrect by these tests? Does adding water increase or decrease the angle of refraction of the light?