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Physics of the Human Eye!!!-Presentation
Transcript of Physics of the Human Eye!!!-Presentation
•The lens How Images are Formed 1. Light waves enter the eye through the cornea
2. Light waves then continue though the pupil and through the lens
3. "Light waves are bent (converged) first by the cornea and then by the lens, to a nodal point" which is right behind the lens
4. At the nodal point, the light wave or the image, turns backwards and upside down
5. "Light waves continue through the vitreous humor, the jelly like substance, and then back to the clear focus on the retina"
6. The light impulses are changed in to electrical signals, which are sent through the optic nerve to the back of the brain
7. Here, the electrical signals are "interpreted or seen by the brain as a visual image" We do not “see” an image with our eyes but rather with the brain. Our eyes are just the beginning step of the visual process. • The lens and magnifications equation can provide an idea of the relationship between the object distance, image distance, and focal length. Lens Equation: 1/f= 1/ do+ 1/di
Magnification Equation: hi/ho = - di/do Example 1: Focal length is 0.018m. Find the image size and image location of a 6-foot tall man (1.83m) who is standing a distance of about 10 feet away (3.05m).
do = 3.05 m ho = 1.83 m f = 0.0180 m
di = ? hi = ?
Determine the image distance:
1/f = 1/do + 1/di
1/ (0.0180 m) = 1/ (3.05 m) + 1/di
55.6 m = 0.328 m + 1/di
55.2 1 = 1/di
di = 0.0181 m = 1.81 cm
Determine the image height:
hi/ho = - di/do
hi /(1.83 m) = - ( 0.0181 m)/(3.05 m)
hi = - (1.83 m) • (0.0181m)/(3.05 m)
hi = -0.0109 m = -1.09 cm Accommodation of the Eye • Accommodation is the ability of the eye to change its focal length
• Typically, "a nearby object is focused at a further distance, the eye accommodates by assuming a lens shape that has a shorter focal length" The reduction in focal length will cause more refraction of light and will bring the image back closer to the cornea/lens system.
The ciliary muscles contract and squeeze the lens into a shorter focal length. • Typically, "a distant object is focused at a closer distance, the eye accommodates by assuming a lens shape that has a longer focal length" The ciliary muscles relax and the lens returns to a flatter shape Eye Defects- Farsightedness Also know as hyperopia
Is the inability of the eye to focus on nearby objects
Results from the weakening of the ciliary muscles and/or the
decreased flexibility of the lens
Two potential causes The lens power to refract light is decreased
The image of nearby objects are focused at a location behind the retina Cure Use of converging lens Eye Defects- Nearsightedness • Also known as myopia
• Is the inability of the eye to focus on distant objects
• Will result if the light from distant objects is refracted more than is necessary
• Usually results from a "bulging cornea or an elongated eyeball" Cure Use of diverging lens Lens Equation The image will be 1.09cm tall "(negative values for image height indicates that the image is an inverted image)" and located 1.81cm from the lens.