Here are some of the key important things that we learned yesterday during our fulfilling 8th period physics class:
-Charges in a system may be transfered from one object to another.
-Objects become electrically positive or negative when they have a deficiency or excess amount of e-.
-The formula Q=ne
q= total charge
n= number of elementary charge
e= elementary charge
Coulombs Law: The electrostatic force between two point charges is:
Directly proportional to product of charges, inversely proportional to square of distance between centers.
Formula: Fe= K(q1q2/r^2)
r= distance between centers of q1 and q2
k= electrostatic constant (k= 8.99 x 10^9 n-m^2/c^2
End of post.
Friday, March 7, 2008
Tuesday, March 4, 2008
Keil Kunzer
Mr. Wirth
Physics R
4 March 2008
The Human Eye
The human eye is a very complex structure of our body. Our eye gives a person the sense of sight and vision. The eye helps us decipher objects, colors, and shapes; it also can detect the difference between dim and bright light. There are many different parts to the human eye but the main ones are the iris, pupil, cornea, lens, and retina. Light waves enter the eye first through the cornea which is the clear part in the center of the eye. Then all the light gets processed in the pupil which is part of the iris. There are also many muscles in the eye that allow it to move and allow for our pupils to get bigger or smaller depending on the brightness of light rays. The human eye consists of many different complex parts, without these we would not have the ability of one of our most important senses (Montgomery).Mr. Wirth
Physics R
4 March 2008
The Human Eye
Human vision is an extremely complex and interesting subject. The basic light sensing structure of the eye is the retina, which consists of both rods and cones. The rods and cones process the light through a chemical reaction, which then creates electrical impulses to the eye’s nerve. After the electrical impulses are sent to the nerve, this information is then sent to the brain where it is processed and then interpreted as light. In the cones are three different color sensing pigments. These colors include red, green, and blue color sensitive pigments. The eye can sense any combination of these colors unless a person has a color blindness disorder. Colorblindness occurs when one of the color pigments in the cones are not functioning properly. Colorblindness occurs in females in less than one percent of the population, but in males it occurs in eight percent of the population. The ability to see light and color is an extremely special feature of the human body, and it is something that many people take for granted.
Just because most everyone have the same eye structure, does not mean every human has the same vision. If someone is considered to have normal vision their vision is 20/20. That means the majority of the human population can see what you see at twenty feet. 20/10 vision is better than normal vision because it means you can see twenty feet of what a normal person can see when standing ten feet away from a vision chart. In the United States a person is legally blind when their vision is 20/200. A few vision problems a person might have are nearsightedness or farsightedness. When a person is nearsighted they have difficulty seeing objects that are close to them, which is caused by an elongated eyeball. The opposite is true for farsighted people, which is when people have trouble seeing objects farther away from them caused by a shorter eyeball. Another vision problem a person might develop is an astigmatism. An astigmatism is when the cornea is uneven or curved. This causes distortion to a person’s vision, yet this can be corrected with a lens that is fitted to correct the uneven cornea. The human vision system is an extremely complex structure of the human body (Bianco).
The human eye is an amazing organ, and gives people the great sense of vision. There are many people who are unable to see the everyday occurrences in their lives due to vision problems. It would be extremely difficult to live not being able to comprehend colors and frequencies of light.
Works Cited
Bianco, Carl. "How Vision Works." How Stuff Works. 4 March 2008
<http://health.howstuffworks.com/eye.htm>
Montgomery, Ted. "Anatomy, Physiology and Pathology of the Human
Eye." 4 March 2008 <http://health.howstuffworks.com/eye.htm>
The Human Eye
Luke Seavitt
Physics blog post
Wirth
The Eye:
Although the human eye is one of the smallest human organs it is one of the most complex. It is composed of several different parts that all work together to help us see the objects that we look at. In order for the eye to maintain its shape it has something called the sclera which is the outermost layer of the eye. The front sixth of the sclera is called the cornea and this part of the eye is also clear. All light that is seen by the human eye has to pass through the cornea. Also attached to the sclera are muscles that provide movement to the eye. These muscles are called extrocular muscles. Blood vessels that supply blood to the eye are located in the second layer of the eye which is called the choroid. The front part of the choroid is composed of two parts the ciliary body and the iris. The ciliary body contracts and relaxes to control the size of the lens for focusing. The iris is the colored part of your eye and is determined by the color of the tissue and pigment cells. The iris itself has two muscles. It has the dilator muscle which makes the pupil larger allowing more light through the eye and making the iris smaller. The sphincter does the opposite of the dilator and makes the pupil smaller by increasing the size of the iris allowing for less light to go through the eye. The intermost layer of the eye is the retina which is the light sensing part of the eye. It contains cells called rod cells that are in charge of vision in low light. It also has cone cells which are responsible for color vision and detail. Another part of the retina is located in the back called the macula. In the center of the retina is something called the fovea centrails which is responsible for seeing small details. Also in the retina is something called the rhodopsin that converts light into electrical impulses to send to the brain to interpret the visions. The retina also has nerve fibers at the back of the eye which form the optic nerve, which conducts the electrical impulses to the brain. The spot where the optic nerve and blood vessels exit the retina is called the optic disk. This area is a blind spot on the retina because there are no rods or cones at that location. However, you are not aware of this blind spot because each eye covers for the blind spot of the other eye. In order for the scela to move the eye it has six different muscles to move the eye. The medial rectus which moves the eye towards the nose and the lateral rectus which does the opposite of the medial rectus and moves the eye away from the nose. It also has the superior rectus which raises the eye and the inferior rectus which lowers the eye. Lastly it has the superior oblique and inferior oblique which both rotate the eye.
Light and Color:
The eye perceives light first through the cornea then the aqueous humor, lens and vitreous humor. Eventually the light reaches the retina which is the light sensing structure. It contains two cells which are rods and cones. The rods handle the vision in low light and the cones handle color vision and detail. When light contacts these two types of cells, a series of complex chemical reactions occurs. This creates electrical impulses that in the optic nerve. In order to see color the eye has color responsive chemicals in the cones called cone pigments and they are very similar to those found in the rods. The retinal portion of the chemical is the same, however the scotopsin is replaced with photopsins. There are three kinds of color-sensitive pigments, red, green, and blue sensitive pigments. Each cone has one of these pigments so it is sensitive to that color. The peak absorbancy of blue-sensitive pigment is 445 nanometers, for green-sensitive pigment it is 535 nanometers, and for red-sensitive pigment it is 570 nanometers.
Refraction:
The eye has multiple angulated surfaces that cause light to bend. These are the interface between the air and the front of the cornea, the interface between the back of the cornea and the aqueous humor. Also the interface between the aqueous humor and the front of the lens and the interface between the back of the lens and the vitreous humor. When every one of these are working perfectly, light makes it through these four interfaces and arrives at the retina in perfect focus.
Normal Vision and Vision Problems:
The normal vision of a human being is 20/20 vision. This is determined by looking at the Snellen eye chart at a distance of 20 feet. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see. However, not all people have perfect 20/20 vision. People can be nearsighted or farsighted meaning that they can either only see up close or they can only see from far away. To fix their vision many people wear eye glasses or contacts. There is also another problem that can occur with the eye called Astigmatism, which is an uneven curvature of the cornea and causes a distortion in vision. To correct this, a lens is shaped to correct the unevenness.
Bianco Md., Dr. Carl. "How Vision Works." How Stuff Works. 1998. 4 Mar. 2008 .
Myers, David G. Psycgolgy . VIII. New York: Worth Publishers, 2007.
Sunday, March 2, 2008
Fiber Optics - John Tedesco
John Tedesco
Mr. Wirth
Physics R
3 March 2008
Physics Blog Post: Fiber Optics
Fiber Optic Cables are one of the most widely used forms of sending information in the twenty first century. Fiber Optic cables are one of the fastest ways of communication, whether it is through the internet, television, or other devices such as telephone (How). In addition, they are very reliable and efficient, drawing more and more companies to use them each year. Millions of Americans use fiber optics in their internet cables instead of DSL. In addition, fiber optic powered internet is light years faster than road runner, something we think is fast. Many major Metropolitan cities such as
Many people are not familiar with this new and efficient technology. Fiber optics is a thin piece of glass about the same size of a single human hair. These thin strands of glass are packaged together in cables and are used to transfer information. Fiber optics consists of three main parts. The core is in the center and is pure, thin glass used to carry the light through the cable. Around the core is the cladding, which provides as a barrier in order to keep the light inside of the core (How). This is able to occur due to total internal reflection, which is when light is unable to escape from the core because of the properties of the cladding. If light tries to escape the core and move onto the cladding, it is unable to due to the difference in the indices of refraction between the core and the cladding (Homework). Surrounding the cladding is the buffer coating, whose only function is to minimize damage to the fiber optics. Thousands of fiber optic cables are then bundled up and are surrounded by jackets, making them the cables that we know today.
[img]http://static.howstuffworks.com/gif/fiber-optic-fiber.jpg[/img]
There is a vast amount of physics behind the uses of fiber optics. All of it surrounds the principle of total internal refection. Total internal reflection is when light cannot pass from one medium to another because of the differences in the indices of refraction. In fiber optics, light is trapped in the core, because the angle of incidence at the surface of the cladding is greater than the critical angle (Homework). This means that the light remains trapped inside of the core and continues to travel at 300,000,000m/s through the cable. This results in the most efficient and by far the most affordable form of communication in the world today.
[img]http://hsc.csu.edu.au/senior_science/core/info_systems/9_4_6/Laserpath.gif[/img]
Fiber optics holds many advantages when compared to other forms of communication present in modern times. It is more efficient, less expensive, it takes up less space, it is faster, it is non-flammable since it uses light instead of electricity, it uses less power, and it can be used in medical imaging (How).
Fiber optics is by far one of the most promising technologies of the day. Taking advantage of light, fiber optics is one of the fastest forms of communication in the world, and it holds promising results for the future.
Citation
"Homework Help: Science: Physics: Fiber Optics." Jiskha Homework Help. 2 Mar 2008
"How Fiber Optics Work." How Stuff Works. 2 Mar 2008
The Human Eye
Mary Posman
The Human Eye
The eye is an intricate and sophisticated structure that enables humans to perceive the world; without which our world, literally, would be dark.
The eye has many complex sections that work together to create the images that we see everyday. Generally the eye is approximately one inch wide, one inch deep and 0.9 inches tall. The sclera is the outermost layer of the eye and its function is to maintain the shape of the eye. Six muscles are attached to the sclera that work together to control the movements of the eye: the medial rectus, which moves the eye towards the nose, the lateral rectus which moves the eye away from the nose, the superior rectus, which raises the eye, the inferior rectus, which lowers the eye, and the superior and inferior oblique, both of which rotate the eye (Bianco). Covering the sclera is a mucus membrane, called conjunctive, which keeps the eye moist.
The cornea is the clear, frontal section of the sclera, which allows light to pass into the eye. The second layer of the eye is the choroid, and supplies blood to the eye. The choroid is composed of two sections, the ciliary body and the iris. The ciliary body is a muscular section attached to the lens, it controls the focusing of the lens by contracting and relaxing. It also produces a liquid solution called aqueous humor, which is located in the front of the eye. The aqueous humor is one of two liquid solutions found in the eye, the other is vitreous humor, which is a gel like substance located in the back section of the eye. The iris is the colored part of the eye and contains two muscles, the dilator and the sphincter. When the dilator contracts, it makes the iris smaller, while the sphincter relaxes to make the iris larger. This controls the amount of light that is let into the eye through the pupil. The picture to the left is an example of the dilator at work, the iris is large, making the pupil small. While on the right is an example of the sphincter, the iris is small, making the pupil larger (Your).
The innermost layer of the eye is the retina, the retina is the light sensing area of the eye. Within the retina there are cells called cones and rods, which detect color and shapes respectively. There are approximately one hundred and fifty million cones and rods in the retina (Your). Both of these are important to our visual processing and will be discussed in more detail later on. The macula is also found in the retina, it is in the center of the retina, the macula contains the fovea centralis, which only houses cones. There is also the chemical rhodopsin, or “visual purple” within the retina, which converts light into electrical impulses that are sent to the brain for interpretation (Bianco). The electrical impulses are carried to the brain by the optic nerve, this is the collection of retinal nerve fibers that collect at the back of the eye. Passing through the optic disk , which is where the optic nerve and blood vessels exit the retina on their way to the brain.. When all of these sections are put together, the eye is formed and fully operational.
Like the eye itself, the process by which humans are able to perceive light and color is also complex. When we perceive light, it must first pass through the cornea, then the aqueous humor, lens and vitreous humor before reaching the retina (Bianco). The light is refracted slightly by the aqueous humor, then a little bit more by the lens and vitreous humor. The lens is responsible for forming the shape of the image, it is able to adjust quickly to different objects by the process of accommodation. The ciliary muscle relaxes and contracts, changing the shape of the lens to adjust to the objects size and distance (Polarization). Once the light reaches the retina it comes in contact with rods and cones, this contact causes chemical reactions to begin in the eye. Activated rhodopsin is created, as mentioned before this generates electrical impulses to the optic nerve. When light enters the rods, it contacts rhodopsin and causes it to decompose into all-trans retinal, which is unstable and decomposes further to metarhodospin II. This is the chemical that actually creates the electrical impulses that are transmitted to the brain (Bianco). When these messages are perceived in the brain, they appear upside down, it is then the brain’s job to flip the images right-side up, this process occurs in the visual cortex (Your).
While the process of perceiving light mainly occurs in the rods, the perception of color takes place largely in the cones. The actual process of perceiving color is similar to that of light, the main difference is that the chemical photopsin replaces scotopsin (see chart above). Also, there are three color-sensitive pigments within the cones, these pigments sense red, green and blue. Each cone has one of these pigments and by various blends of these pigments, we are able to perceive almost any color (Bianco). Both of these processes occur at the same time, allowing humans to perceive the light, shapes and colors of the world.
When all is functioning properly, humans are able to “see” the world around them clearly and in focus. Visual acuity is tested by the Snellen eye chart, which is a chart of letters in rows, decreasing in size from the top row.
http://www.contrastsensitivity.net/images/echart.jpg
Normal vision is defined as 20/20, which means that at twenty feet away from the chart you can see the same amount of accurate letters as most people see from twenty feet. 20/40 means that you have less than normal visual acuity and can only see what most people can see at forty feet away. It is possible to have better than normal vision, 20/10 for example. This means that at twenty feet you can see what most people can only see at ten feet away (Bianco). Depth perception is another part of normal vision, this enables humans to decipher how far away an object is. There are three main processes by which humans determine an object’s depth/distance. The first is the amount of space the object takes on the retina. If the object takes a large place on the retina, the brain will determine that it is closer, while an object that is farther away would take up less space on the retina. Secondly, when we move our head side to side, objects that are close to us move rapidly across our retina, and appear as a blear moving past us, while those that are farther away move across our retina at a slower pace and appear more clearly (Bianco). Here’s an example, imagine that you are looking out the car window, the trees that are right at the edge of the road appear in a blur of green and brown, while we can clearly see those that are farther away. Thirdly there is stereo vision, each eye receives a different image since they are about an inch apart. The brain interprets the differences in these images to determine the location of the object (Bianco).
Since the process of vision is complex, there can be many errors and problems that occur. One of which is color blindness, this is the inability to differentiate between colors. This affliction is more common in men, since it is an inherited effect and the capacity of color vision is in the X-chromosomes and women have two. The most common type of color blindness is the inability to differentiate between red and green. In this case either the red or green cones are not present or they do not function properly (Bianco).
http://www.colormatters.com/kids/images/cones_color.jpg
Another failure in vision is night blindness, which is caused by vitamin A deficiency. Vitamin A is necessary to form retinal, a part of the rhodopsin molecule that that senses light. A lack of these light sensing molecules causes an inability to see at night, since there is not enough light (Bianco). This is less common, but its does still occur. Astigmatism is more common, especially as people age, and is a curvature of the cornea that distorts vision. This can be corrected by creating a contact lens that corrects the curvature of the cornea. Troubles with refraction also cause visual problems such as nearsightedness and farsightedness. Nearsightedness, or myopia, is when a person can see things clearly up close, but not far away. This is caused by an eyeball that is, in essence, too long.
(Your)
The light rays don not quite reach the retina, and are focused instead, on the front of the retina. This can be corrected with concave-lenses, which will cause the light to diverge slightly before reaching the eye (Bianco).
Farsightedness, or hyperopia, is when a person can see things at a distance, but not close up. This, is the opposite of nearsightedness and is caused by an eyeball that is too short.
(Your)
The shortness of the eyeball causes the light rays to go pass the retina. This can be corrected with convex lenses (Bianco).
While these are minor problems that can be corrected for the most part, there are also many causes of blindness.
Blindness is technically defined as vision that is less than 20/200 and can have many different causes. One such cause is cataracts, which are cloudy substances that form on the lens, preventing light from reaching the retina. These are more common with age and can be corrected with surgery.
http://www.ehponline.org/docs/2005/113-3/eye.jpg
Glaucoma is another cause a blindness, this occurs when the aqueous humor does not drain correctly, causing pressure to build up in the eye killing cells and nerve fibers in the back of the eye. This can also be corrected with surgery or medicine (Bianco). Diabetic retinopathy also causes blindness in people with diabetes. It occurs when there is a blockage, leakage and/or scaring of blood vessels in the eye. However, it can be cured with laser surgery. There is also macular degeneration, the macular is responsible for fine-detailed vision, it begins to deteriorate, and eventually all central vision is lost. Sometimes this can he helped with laser surgery, but not always (Bianco). Trachoma is an infection that is caused by Chlamydia trachomais and eventually leads to blindness, however it can be cured with antibiotics. Another form of blindness is caused by retinitis pigmentosa, an inherited disease that causes blindness by degenerating the retina and excess pigment that allows humans to perceive light. It is a degenerate process, beginning with night blindness, then tunnel vision then complete blindness. There is, unfortunately, no known treatment for this disease. Trauma can also cause blindness, especially if it involves chemical injuries that damage the eye (Bianco). While these are some of the most prevalent causes of blindness, there are many others including strokes and neurological diseases. While these cases of blindness exists, most people are fortunate and have accurate vision, or vision that can be corrected with glasses or contact lenses.
The eye is a fascinating mechanism that is critical to man’s survival. Man’s existence is centered on the proper functioning of the eye, and today we are lucky to have the technology to correct many dysfunctions of the eye. The eye’s processes of vision, and the physics that accompanies it is an intriguing and necessary part of life.
Bibliography
Bianco, Carl. "How Vision Works." How Stuff Works. 26 Feb 2008 http://health.howstuffworks.com/eye.htm.
"Polarization; and The Huamn Eye." PY106-Elementary Physics II. Boston University. 29
Feb2008 http://physics.bu.edu/~duffy/PY106/Eye.html.
"Your Sense of Sight." Think Quest Junior. 29 Feb 2008.
The Human Eye
The eye is an intricate and sophisticated structure that enables humans to perceive the world; without which our world, literally, would be dark.
The eye has many complex sections that work together to create the images that we see everyday. Generally the eye is approximately one inch wide, one inch deep and 0.9 inches tall. The sclera is the outermost layer of the eye and its function is to maintain the shape of the eye. Six muscles are attached to the sclera that work together to control the movements of the eye: the medial rectus, which moves the eye towards the nose, the lateral rectus which moves the eye away from the nose, the superior rectus, which raises the eye, the inferior rectus, which lowers the eye, and the superior and inferior oblique, both of which rotate the eye (Bianco). Covering the sclera is a mucus membrane, called conjunctive, which keeps the eye moist.
The cornea is the clear, frontal section of the sclera, which allows light to pass into the eye. The second layer of the eye is the choroid, and supplies blood to the eye. The choroid is composed of two sections, the ciliary body and the iris. The ciliary body is a muscular section attached to the lens, it controls the focusing of the lens by contracting and relaxing. It also produces a liquid solution called aqueous humor, which is located in the front of the eye. The aqueous humor is one of two liquid solutions found in the eye, the other is vitreous humor, which is a gel like substance located in the back section of the eye. The iris is the colored part of the eye and contains two muscles, the dilator and the sphincter. When the dilator contracts, it makes the iris smaller, while the sphincter relaxes to make the iris larger. This controls the amount of light that is let into the eye through the pupil. The picture to the left is an example of the dilator at work, the iris is large, making the pupil small. While on the right is an example of the sphincter, the iris is small, making the pupil larger (Your).
The innermost layer of the eye is the retina, the retina is the light sensing area of the eye. Within the retina there are cells called cones and rods, which detect color and shapes respectively. There are approximately one hundred and fifty million cones and rods in the retina (Your). Both of these are important to our visual processing and will be discussed in more detail later on. The macula is also found in the retina, it is in the center of the retina, the macula contains the fovea centralis, which only houses cones. There is also the chemical rhodopsin, or “visual purple” within the retina, which converts light into electrical impulses that are sent to the brain for interpretation (Bianco). The electrical impulses are carried to the brain by the optic nerve, this is the collection of retinal nerve fibers that collect at the back of the eye. Passing through the optic disk , which is where the optic nerve and blood vessels exit the retina on their way to the brain.. When all of these sections are put together, the eye is formed and fully operational.
Like the eye itself, the process by which humans are able to perceive light and color is also complex. When we perceive light, it must first pass through the cornea, then the aqueous humor, lens and vitreous humor before reaching the retina (Bianco). The light is refracted slightly by the aqueous humor, then a little bit more by the lens and vitreous humor. The lens is responsible for forming the shape of the image, it is able to adjust quickly to different objects by the process of accommodation. The ciliary muscle relaxes and contracts, changing the shape of the lens to adjust to the objects size and distance (Polarization). Once the light reaches the retina it comes in contact with rods and cones, this contact causes chemical reactions to begin in the eye. Activated rhodopsin is created, as mentioned before this generates electrical impulses to the optic nerve. When light enters the rods, it contacts rhodopsin and causes it to decompose into all-trans retinal, which is unstable and decomposes further to metarhodospin II. This is the chemical that actually creates the electrical impulses that are transmitted to the brain (Bianco). When these messages are perceived in the brain, they appear upside down, it is then the brain’s job to flip the images right-side up, this process occurs in the visual cortex (Your).
While the process of perceiving light mainly occurs in the rods, the perception of color takes place largely in the cones. The actual process of perceiving color is similar to that of light, the main difference is that the chemical photopsin replaces scotopsin (see chart above). Also, there are three color-sensitive pigments within the cones, these pigments sense red, green and blue. Each cone has one of these pigments and by various blends of these pigments, we are able to perceive almost any color (Bianco). Both of these processes occur at the same time, allowing humans to perceive the light, shapes and colors of the world.
When all is functioning properly, humans are able to “see” the world around them clearly and in focus. Visual acuity is tested by the Snellen eye chart, which is a chart of letters in rows, decreasing in size from the top row.
http://www.contrastsensitivity.net/images/echart.jpg
Normal vision is defined as 20/20, which means that at twenty feet away from the chart you can see the same amount of accurate letters as most people see from twenty feet. 20/40 means that you have less than normal visual acuity and can only see what most people can see at forty feet away. It is possible to have better than normal vision, 20/10 for example. This means that at twenty feet you can see what most people can only see at ten feet away (Bianco). Depth perception is another part of normal vision, this enables humans to decipher how far away an object is. There are three main processes by which humans determine an object’s depth/distance. The first is the amount of space the object takes on the retina. If the object takes a large place on the retina, the brain will determine that it is closer, while an object that is farther away would take up less space on the retina. Secondly, when we move our head side to side, objects that are close to us move rapidly across our retina, and appear as a blear moving past us, while those that are farther away move across our retina at a slower pace and appear more clearly (Bianco). Here’s an example, imagine that you are looking out the car window, the trees that are right at the edge of the road appear in a blur of green and brown, while we can clearly see those that are farther away. Thirdly there is stereo vision, each eye receives a different image since they are about an inch apart. The brain interprets the differences in these images to determine the location of the object (Bianco).
Since the process of vision is complex, there can be many errors and problems that occur. One of which is color blindness, this is the inability to differentiate between colors. This affliction is more common in men, since it is an inherited effect and the capacity of color vision is in the X-chromosomes and women have two. The most common type of color blindness is the inability to differentiate between red and green. In this case either the red or green cones are not present or they do not function properly (Bianco).
http://www.colormatters.com/kids/images/cones_color.jpg
Another failure in vision is night blindness, which is caused by vitamin A deficiency. Vitamin A is necessary to form retinal, a part of the rhodopsin molecule that that senses light. A lack of these light sensing molecules causes an inability to see at night, since there is not enough light (Bianco). This is less common, but its does still occur. Astigmatism is more common, especially as people age, and is a curvature of the cornea that distorts vision. This can be corrected by creating a contact lens that corrects the curvature of the cornea. Troubles with refraction also cause visual problems such as nearsightedness and farsightedness. Nearsightedness, or myopia, is when a person can see things clearly up close, but not far away. This is caused by an eyeball that is, in essence, too long.
(Your)
The light rays don not quite reach the retina, and are focused instead, on the front of the retina. This can be corrected with concave-lenses, which will cause the light to diverge slightly before reaching the eye (Bianco).
Farsightedness, or hyperopia, is when a person can see things at a distance, but not close up. This, is the opposite of nearsightedness and is caused by an eyeball that is too short.
(Your)
The shortness of the eyeball causes the light rays to go pass the retina. This can be corrected with convex lenses (Bianco).
While these are minor problems that can be corrected for the most part, there are also many causes of blindness.
Blindness is technically defined as vision that is less than 20/200 and can have many different causes. One such cause is cataracts, which are cloudy substances that form on the lens, preventing light from reaching the retina. These are more common with age and can be corrected with surgery.
http://www.ehponline.org/docs/2005/113-3/eye.jpg
Glaucoma is another cause a blindness, this occurs when the aqueous humor does not drain correctly, causing pressure to build up in the eye killing cells and nerve fibers in the back of the eye. This can also be corrected with surgery or medicine (Bianco). Diabetic retinopathy also causes blindness in people with diabetes. It occurs when there is a blockage, leakage and/or scaring of blood vessels in the eye. However, it can be cured with laser surgery. There is also macular degeneration, the macular is responsible for fine-detailed vision, it begins to deteriorate, and eventually all central vision is lost. Sometimes this can he helped with laser surgery, but not always (Bianco). Trachoma is an infection that is caused by Chlamydia trachomais and eventually leads to blindness, however it can be cured with antibiotics. Another form of blindness is caused by retinitis pigmentosa, an inherited disease that causes blindness by degenerating the retina and excess pigment that allows humans to perceive light. It is a degenerate process, beginning with night blindness, then tunnel vision then complete blindness. There is, unfortunately, no known treatment for this disease. Trauma can also cause blindness, especially if it involves chemical injuries that damage the eye (Bianco). While these are some of the most prevalent causes of blindness, there are many others including strokes and neurological diseases. While these cases of blindness exists, most people are fortunate and have accurate vision, or vision that can be corrected with glasses or contact lenses.
The eye is a fascinating mechanism that is critical to man’s survival. Man’s existence is centered on the proper functioning of the eye, and today we are lucky to have the technology to correct many dysfunctions of the eye. The eye’s processes of vision, and the physics that accompanies it is an intriguing and necessary part of life.
Bibliography
Bianco, Carl. "How Vision Works." How Stuff Works. 26 Feb 2008 http://health.howstuffworks.com/eye.htm.
"Polarization; and The Huamn Eye." PY106-Elementary Physics II. Boston University. 29
Feb2008 http://physics.bu.edu/~duffy/PY106/Eye.html.
"Your Sense of Sight." Think Quest Junior. 29 Feb 2008
weekly blog
This week we mostly did review, which I thought was helpful. This unit has been kind of long, so I think this week of review was a good idea before the test on monday. I really like that you give out review packets and the answers so we can learn what we need to study and what we already know. Hopefully all of this will pay off and the test will go well on Monday.
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