Wednesday, April 9, 2008
Tuesday, April 8, 2008
winter break blog post
Polarization- is a property of trannsverse waves which describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel. This concept is used in areas of science and technology dealing with wave propagation, such as optics, seismology, and telecommunications. In electrodynamics, polarization characterizes electromagnetic waves, such as light, by specifying the direction of the wave's electric field. Longitudinal waves such as sound waves in liquids and gases do not exhibit polarization, because for these waves the direction of oscillation is along (and thus is uniquely determined by) the direction of wave's travel. In contrast, the direction of the (electric field) oscillation in electromagnetic waves is not uniquely determined by the direction of propagation. Similarly, the direction of shear stress in a transverse sound wave in a solid can have any orientation in the plane that is perpendicular to the propagation direction. The term polarization thus describes the possible orientations of the oscillatory process in the plane perpendicular to the transverse wave's path.
Monday, April 7, 2008
Ch. 20 #63
Lucien Rouse
The leyden jar is considered to be the first ever capacitor, and it was invented by Pieter van Musschenbroek. It consisted of a metal outer part, with a brass rod coming out of the top. The brass passes through a wood coating. When a charge is applied, the charge is kept at equilibrium by the metal coating and the wood, and cannot be discharged without further action.
The Wimshurst machine was invented by James Wimshurst to create strong electric charges. Two insulated disks in the center of the machine are what drive it. As they rotate, a strong charge is produced.
i cannot get my pictures to work, but here are the URL's
http://www.rfcafe.com/references/electrical/Electricity%20-%20Basic%20Navy%20Training%20Courses/images/Figure%209.jpg
http://www.sciencefirst.com/pctr/10069.JPG
The leyden jar is considered to be the first ever capacitor, and it was invented by Pieter van Musschenbroek. It consisted of a metal outer part, with a brass rod coming out of the top. The brass passes through a wood coating. When a charge is applied, the charge is kept at equilibrium by the metal coating and the wood, and cannot be discharged without further action.
The Wimshurst machine was invented by James Wimshurst to create strong electric charges. Two insulated disks in the center of the machine are what drive it. As they rotate, a strong charge is produced.
i cannot get my pictures to work, but here are the URL's
http://www.rfcafe.com/references/electrical/Electricity%20-%20Basic%20Navy%20Training%20Courses/images/Figure%209.jpg
http://www.sciencefirst.com/pctr/10069.JPG
Winter Post...well at this point spring break post
THE HUMAN EYE
Our human eye is a complex organ with a variety of layers and muscles. Obviously, it is used to help humans use thier sense of sight.The human eye is unique in that it accommodates for different light intensities and also focuses light rays that come from different distances from the eye. Light is then converted into impulses and sent to the brain where this image is perceived as what it looks like. Vision is very dependent on light. The light rays are reflected off object and then make their way into the eye. The light rays enter the eye through the cornea and the cornea refracts the light as it enters the eye. After passing through the cornea the light rays pass through the opening called the pupil. The iris is the part of the eye that controls the dilation of the pupil. This allows a certain amount of light into the eye. However, many humans experience vision problems that either impair their vision or prevent them from seeing altogether. At 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall, the human eye is composed of fifteen main parts. Maintaining the shape of the eye is the tough, outermost layer the sclera. A clear layer, the cornea, covers the front of the sclera. Light first passes through the cornea when it enters the eye. Attached to the sclera are the extraocular muscles that move the eye. The choroid is the second layer of the eye. It contains the blood vessels that supply blood to all structures of the eye. The choroid is composed of the ciliary body and the iris. A muscular area that is attached to the lens, the ciliary body contracts and relaxes to control the size of the lens for focusing. Functioning to color the eye, the iris is an adjustable diaphragm surrounding the pupil. It has two muscles: the dilator and the sphincter. Both control the amount of light let into the eye by adjusting the pupil size. The color of the iris is determined by the color of the connective tissue and pigment cells. The innermost layer is the retina -- the light-sensing portion of the eye. It contains rod cells, which are responsible for vision in low light, and cone cells, which are responsible for color vision and detail. In the back of the eye, in the center of the retina, is the macula. In the center of the macula is an area called the fovea centralis. This area contains only cones and is responsible for seeing fine detail clearly. Inside the eyeball there are two fluid-filled sections separated by the lens, a clear structure used to fine-tune vision. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor. When drainage of the aqueous humor is blocked, a disease called glaucoma can result. The eye is also unique in that it is able to move in many directions to maximize the field of vision, yet is protected from injury by a bony cavity called the orbital cavity. The eye is embedded in fat, which provides some cushioning. The eyelids protect the eye by blinking. Eyelashes and eyebrows protect the eye from particles that may injure it.There are six muscles attached to the sclera that control the movements of the eye. They are shown here with their descriptions:MusclePrimary FunctionMedial rectusmoves eye towards noseLateral rectusmoves eye away from noseSuperior rectusraises eyeInferior rectuslowers eyeSuperior obliquerotates eyeInferior obliquerotates eyeAfter passing through the cornea, light passes through the aqueous humor, lens and vitreous humor. Ultimately it reaches the retina, which is the light-sensing structure of the eye. The retina is made up of cones and rods and is lined with black pigment called melanin to lessen the amount of reflection. The retina has a central area, called the macula that is responsible for sharp, detailed vision. The color-responsive chemicals in the cones are called cone pigments and are very similar to the chemicals in the rods. Each cone cell has a red-sensitive pigment, a green-sensitive pigment, and a blue-sensitive pigment. The presence of these pigments allow the eye to be sensitive to that color. The human eye can sense almost any gradation of color when red, green and blue are mixed.In the diagram above, the wavelengths of the three types of cones (red, green and blue) are shown. The peak absorbency of blue-sensitive pigment is 445 nanometers, for green-sensitive pigment it is 535 nanometers, and for red-sensitive pigment it is 570 nanometers. Color blindness is the inability to differentiate between different colors. The most common type is red-green color blindness. This occurs in 8 percent of males and 0.4 percent of females. It occurs when either the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. Another vision problem is vitamin A deficiency. When severe vitamin A deficiency is present, then night blindness occurs. This is when the levels of light-sensitive molecules are low due to vitamin A deficiency, there may not be enough light at night to permit vision. During daylight, there is enough light stimulation to produce vision despite low levels of retinal. Refraction is when light rays reach an angulated surface of a different material and the light rays bend. When light reaches a convex lens, the light rays bend toward the center:When light rays reach a concave lens, the light rays bend away from the center:Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. 20/20 vision means when standing 20 feet away from the chart you can see what a "normal" human being can see and have normal vision. If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. 20/200 is the cutoff for legal blindness in the United States. It is also possible to have vision better than normal. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart. Hawks, owls and other birds of prey have much more acute vision than humans. A hawk has a much smaller eye than a human being but has lots of sensors (cones) packed into that space. This gives a hawk vision that is eight times more acute than a human's. A hawk might have 20/2 vision!Normally, your eye can focus an image exactly on the retina:Nearsightedness and farsightedness occur when the focusing is not perfect. When nearsightedness is present, a person can clearly see near objects, while experiencing difficulty seeing far objects. Light rays become focused in front of the retina. This is caused by an eyeball that is too long, or a lens system that has too much power to focus. Nearsightedness is corrected with a concave lens. This lens causes the light to diverge slightly before it reaches the eye, as seen here:When farsightedness is present, a person can clearly see far objects, but has trouble seeing seeing near objects. Light rays become focused behind the retina. This is caused by an eyeball that is too short, or by a lens system that has too little focusing power. This is corrected with a convex lens, as seen here:As stated earlier, to be legally blind visual acuity must be less than 20/200 with corrective lenses. Some causes of blindness include cataracts, glaucoma, macular degeneration, trauma, vitamin A deficiency, tumors, strokes, neurological diseases, hereditary diseases and toxins.The human eye is an interesting organ full of potential complications and great physics lessons.
Sunday, April 6, 2008
Winter Blog Post
Physics Explained: Rainbows, Mirages, Color of Sky & Sunsets.
*To understand the phenomenon of rainbows, mirages, and the color of the sky and sunsets, we must first look at understand the concepts of how light and optics work.
*Speed of light in a medium is determined by the interactions between light and the atoms that make up any particular medium. Some terms to familiarize ourselves with are index of refraction and reflection. The index of refraction is in a medium, the ration of the speed of light in a vacuum to the speed of light in that medium. Reflection occurs when light traveling from a region strikes a boundary at an angle and produces a wave that is bounced off of that boundary.
*A mirage can occur on a summer day. When you are driving down the road you see a looks to be a reflection of an oncoming car in a pool of water. However, the pool disappears as you begin to approach it. This mirage is the result of the Sun heating the road. The extremely hot road heats the air above it and a thermal layering of air is produced, which causes any light traveling towards the road to gradually bend upwards. This makes the light appear to be coming from a reflection in a pool on the road.
Basically...a mirage is seen on the surface of the road. Light bends upwards into the eye of the observer and the bottom of the wave front moves faster than the top-creating the mirage.
*Another concept we must identify is dispersion. Dispersion is when white light separates into a spectrum of colors when it passes through a glass prism. White light that is directed through a prism is dispersed into bands of different colors. The different colors of light bend different amounts when they enter into a medium. Different colors of visible light have different speeds when going through a medium.
*A prism is not the only way of dispersing light. A rainbow is actually a spectrum formed when sunlight is dispersed by water in the atmosphere (light rain or humidity). Sunlight that later falls on the water droplets is refracted and because of dispersion each color is refracted at different angles. And back at the top of the surface of the water droplet some light fore goes internal reflection and on the way
out of the droplet the light is again refracted and dispersed.
Basically...a rainbow forms when white light is dispersed as it enters and reflects at the inside boundaries and exits through a rain droplet. And due to dispersion only one color from each raindrop reaches an observer-creating a rainbow.
Work Cited:
1. Glencoe Science, Physics Principles and Problems Text Book. (Our textbook)
#63
History of Science:
*The Leyden Jar:
*a German scientist named Ewald Georg von Kleist invented the capacitor in November of 1745
*a little while later a Dutch professor, Pieter van Musschenbroekcame up with a very similar device called the Leyden Jar
*this is typically thought as the first capacitor
*this is generally a simple device
* it is made up of a glass jar, half filled with water and lined inside and out with metal foil
-(the glass acts as the dielectric)
-(water used to be thought to be the key ingredient)
*there was usually a metal wire or chain driven through a cork in the top of the jar
*the chain was then hooked onto something that would give a charge
-(probably a hand-cranked static generator)
*once the charge was delivered the jar would hold 2 equal (opposite) charges in equilibrium until they were connected with a wire...which would produce a small spark or shock
*The Leyden Jar:
*a German scientist named Ewald Georg von Kleist invented the capacitor in November of 1745
*a little while later a Dutch professor, Pieter van Musschenbroekcame up with a very similar device called the Leyden Jar
*this is typically thought as the first capacitor
*this is generally a simple device
* it is made up of a glass jar, half filled with water and lined inside and out with metal foil
-(the glass acts as the dielectric)
-(water used to be thought to be the key ingredient)
*there was usually a metal wire or chain driven through a cork in the top of the jar
*the chain was then hooked onto something that would give a charge
-(probably a hand-cranked static generator)
*once the charge was delivered the jar would hold 2 equal (opposite) charges in equilibrium until they were connected with a wire...which would produce a small spark or shock
Scribe 3.31.08
ANALYSING CIRCUITS:
Series Circuit:
*a series circuit in which there is only one current path with multiple drops in potential along the path
*(ex) Christmas lights not working
Current in a Series Circuit:
*the current is the same in all components of a series circuit
*I=I1=I2=I3=...
Potential in a Series Circuit:
*the sum of the potential drops in a series circuit is equal to the source potential
*V=V1+V2+V3+...
Resistance in a Series Circuit:
*the equivalent resistance of a series circuit is equal to the sum of the resistance of its components
*Req=R1+R2+R3+...
*ammeters must be connected in series
-all current has to flow through it
SERIES CURRENT SUMMARY:
*only 1 path
*derivation of series circuit Req
*Given V=V1+V2+V3+... where V=IR
*Then IReq=I1R1+I2R2+I3R3+...
*But I=I1=I2=I3=...
*So Req=R1+R2+R3+...
Parallel Circuits:
*a parallel circuit is one in which there is only one potential drop with multiple paths for current to flow across the potential drop
Current in a Parallel Circuit:
*total current in a parallel circuit is the current supplied by the source and is equal to the sum of the branch current
*I=I1+I2+I3+...
Potential in a Parallel Circuit:
*the potential drop across each branch of a parallel circuit is the same as the source potential
*V=V1=V2=V3=...
Resistance in a Parallel Circuit:
*the reciprical of Req of a parallel circuit is equal to the sum of the recipricals of the brance resistance
*1/Req=1/R1+1/R2+1/R3+...
*Voltmeters must be connected in parallel
Series Circuit:
*a series circuit in which there is only one current path with multiple drops in potential along the path
*(ex) Christmas lights not working
Current in a Series Circuit:
*the current is the same in all components of a series circuit
*I=I1=I2=I3=...
Potential in a Series Circuit:
*the sum of the potential drops in a series circuit is equal to the source potential
*V=V1+V2+V3+...
Resistance in a Series Circuit:
*the equivalent resistance of a series circuit is equal to the sum of the resistance of its components
*Req=R1+R2+R3+...
*ammeters must be connected in series
-all current has to flow through it
SERIES CURRENT SUMMARY:
*only 1 path
*derivation of series circuit Req
*Given V=V1+V2+V3+... where V=IR
*Then IReq=I1R1+I2R2+I3R3+...
*But I=I1=I2=I3=...
*So Req=R1+R2+R3+...
Parallel Circuits:
*a parallel circuit is one in which there is only one potential drop with multiple paths for current to flow across the potential drop
Current in a Parallel Circuit:
*total current in a parallel circuit is the current supplied by the source and is equal to the sum of the branch current
*I=I1+I2+I3+...
Potential in a Parallel Circuit:
*the potential drop across each branch of a parallel circuit is the same as the source potential
*V=V1=V2=V3=...
Resistance in a Parallel Circuit:
*the reciprical of Req of a parallel circuit is equal to the sum of the recipricals of the brance resistance
*1/Req=1/R1+1/R2+1/R3+...
*Voltmeters must be connected in parallel
Friday, April 4, 2008
#63...Better late than never
The Leyden jar was created in 1746. It was made of a glass jar with an outer and inner metal coating. An external brass rod passes through a wooden stopper and is connected to the inner coating by a conductive chain. When an electrical charge is applied to the external knob, positive and negative charges come from the two metal coatings respectively, but the insulative glass prevents them from discahrging. This results in the charges holding each other at equilibrium until a discharge path is provided. These jars were first used to store electricity in experiments and later as a condenser in early wireless equipment. In essence the layden jar was the first battery!!!
Thursday, April 3, 2008
What we learned in Physics 4/2
Resistance in a Conductor
- The resistance of a conductor increases as it gets: longer, thinner, hotter
- Wires are better conductors when they are short, fat
- L is the length
- A is the area
"l" is the length
"A" is the cross sectional area
"ρ" is the resistivity of the material (found in reference table)
Friday, March 28, 2008
March 28th-A Day of Physics
10:45 AM
*Mr. Wirth wonderfully volunteers me to be scribe. . .
10:47AM
*Begin going over the homework
Example work for #3-
Given Info:
q = 220 C
v = 220 V
t = 4 sec
ESA work:
P = VI
P = V [(delta q)/t]
P = (2200 C)(220 V) /(4 s)
P = 12,100 W
10:55 AM
*Begin notes
*Analyzing Circuits
-several different configurations
-branches
-involves Ohm's Law (applies to circuit and individual resistors)
***Equivalent Resistance: The Resistance Seen By The Source***
R(eq) = V(source) / I (source)
10:58 AM
*Talk about Next Week
-will apply these principals to several different circuit configurations
10:59 AM - 11:00 AM
*Talk about new cell phone policy and pass out the review set #1
11:07 AM
*Still working on review set
11:25 AM
*class ends; have a nice weekend :)
-DH
*Mr. Wirth wonderfully volunteers me to be scribe. . .
10:47AM
*Begin going over the homework
Example work for #3-
Given Info:
q = 220 C
v = 220 V
t = 4 sec
ESA work:
P = VI
P = V [(delta q)/t]
P = (2200 C)(220 V) /(4 s)
P = 12,100 W
10:55 AM
*Begin notes
*Analyzing Circuits
-several different configurations
-branches
-involves Ohm's Law (applies to circuit and individual resistors)
***Equivalent Resistance: The Resistance Seen By The Source***
R(eq) = V(source) / I (source)
10:58 AM
*Talk about Next Week
-will apply these principals to several different circuit configurations
10:59 AM - 11:00 AM
*Talk about new cell phone policy and pass out the review set #1
11:07 AM
*Still working on review set
11:25 AM
*class ends; have a nice weekend :)
-DH
Wednesday, March 26, 2008
3/26/08 Class Notes
AC = alternating current. The flow of the current alternates direction
DC= direct current. Only flows in one direction
We will only be working with DC.
Current (I)= the flow of an electric charge. Unit: ampere (A) or coulomb/second.
The equation for current is listed in the reference table as I=(change in q)/(t)
Potential difference (V)= the driving force behind causing a flow of charge.
SI Unit: volt (V)
1 V=1 J/C
The equation to find V is V = W/q
Resistance (R)= oppostition to the flow of the current. It measures the degree and object opposes a current
SI Unit: ohm (theres a funky symbol in the reference table for it) which was named after a German physicist
Ohm's Law: At Constant Temperature, The Current In A Metallic Conductor Is Directly Proportional To The Potential Difference Between Its Ends.
The equations for Ohm's law are as follows... R=V/I....I=V/R.....V=IR
1 ohm = 1 Volt/Amp
We did two exaples in class and then worked on homework for the time we had left.
DC= direct current. Only flows in one direction
We will only be working with DC.
Current (I)= the flow of an electric charge. Unit: ampere (A) or coulomb/second.
The equation for current is listed in the reference table as I=(change in q)/(t)
Potential difference (V)= the driving force behind causing a flow of charge.
SI Unit: volt (V)
1 V=1 J/C
The equation to find V is V = W/q
Resistance (R)= oppostition to the flow of the current. It measures the degree and object opposes a current
SI Unit: ohm (theres a funky symbol in the reference table for it) which was named after a German physicist
Ohm's Law: At Constant Temperature, The Current In A Metallic Conductor Is Directly Proportional To The Potential Difference Between Its Ends.
The equations for Ohm's law are as follows... R=V/I....I=V/R.....V=IR
1 ohm = 1 Volt/Amp
We did two exaples in class and then worked on homework for the time we had left.
Tuesday, March 25, 2008
3/25/08 Notes
Electrical Circuits:
- Closed loop or path
- Consist of charged particles that move
- An electrical current can exist
- Are formed by a source of potential difference and includes one or more resistances
Circuit Elements:
- Source elements - device or system that can produce a potential difference.
- Load elements - device or system to which the source is connected.
- Control elements - used to control the flow of electrical current.
- Path elements - used to interconnect other elements.
Circuit Symbols:
Current:
- The flow of electric charge.
- The time-rate at which charge flows past a given point in a circuit.
- SI unit: ampere (A)
- 1 ampere = 1 coulomb/second
- 1A = 1C/s
Monday, March 24, 2008
The Leyden Jar...Finally
The Leyden Jar is a capacitor, it stores electricity. There is an electrode on the top of the jar, and a chain is attached to it. The jar becomes charged by static electricity buildup in the inner electrode, while the outer part of the jar is grounded. The Leyden Jar was used in early wireless technology.
March 17th- class notes
In class we went over electrical potential, what a volt is and uniform electric field. A volt is the SI derived unit for electrical potential. Electrical potential may be conceived as "electric pressure". Where this pressure is uniform , no current flows and nothing happens. This is similar to why people do not feel normal atmospheric pressure. However when this electric pressure varies, an electric field exists, which creates a force on charges particles.
Monday, March 17, 2008
Problem 63
The Leyden jar originated in 1746. It consists of a glass jar with an outer and inner metal coating covering the bottom and sides up to the neck. A brass rod in an external knob passes through a wooden stopped and is connected to the inner coating by a loose chain. When an electrical charge is applied to the external knob, positive and negative charges come from the two metal coatings respectively, but they are unable to discharge because of the glass between them. This results in the charges holding each other at equilibrium until a discharge path is provided. These jars were first used to store electricity in experiments and later as a condenser in early wireless equipment.
The Wimshurst machine is an electrostatic device used to generate high voltages between 1880 and 1883 by British inventor James Wimshurst. In this machine, the two insulated disks and their metal sectors rotate in opposite directions passing the crossed metal neutralizer bars and their brushes. An imbalance of charges is then induced, amplified and collected by two pairs of metal combs with points placed near the surfaces of each disk. These collectors are mounted on insulating supports and connected to the output terminals. The positive feedback increases the charges exponentially until the dielectric breakdown voltage of the air is reached and a spark jumps across the gap.
Winter Break Blog Post....
The Human EyeThe human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four sense. In order to understand how the human eye works, one must understand the anatomy of the eye. When you look at an object, light rays are reflected from the object to the cornea (a clear dome at the front of the eye), these rays are bent, refracted and focused by the cornea, lens and vitreous. The lens makes sure the rays come to sharp focus on the retina. When the image gets to the retina it is upside down. The light rays are then converted to electrical impulses which are then transmitted through the optic nerve, and to the brain where the image is translated and shown in an upright position. The amount of light entering the eye is controlled by the iris which lies in between the cornea and lens. Rays of light entering your eye are bent first by the curved transparent cornea, pass through the liquid aqueous humor and the hole through your muscular iris called the pupil, are further bent by the lens, and pass through your transparent vitreous humor before focusing on the rods and cons in the back of your eye. When it suddenly become dark, your gradual increase in sensitivity to the low level of light (dark adaptation) results from a shift from a predominantly cone vision to predominantly rod vision. In bright light, just one cone can stimulate a bipolar cell sufficiently to fire, providing greater visual acuity or resolution.
The colors of objects you see depend on the wavelengths of light reflected from those objects to your eyes. Light is the visible portion of the electromagnetic spectrum. When looking at ROYGBIV (red, orange, yellow, green, blue, indigo, violet) the colors vary in wavelength from the longest (red) to the shortest (violet). When light hits an object, different wavelengths of light can be reflected, transmitted, or absorbed. The more lightwaves your eyes receive (the higher the amplitude of the wave), the brighter an object appears. The wavelengths of light that reach your eye from the object determine the color, or hue, the object appears to be.
Vision is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a “normal” human being should be able to see when standing here. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a “normal” person can see. If you have 20/40 vision, it means that when you stand 20 feet away from the chart, you can only see what a normal human can see when standing 40 feet from the chart.
There are many different types of vision problems. Some of the more common problems are the following:
Amblyopia, Strabismus:
This occurs when one eye turns in or out, up or down, or there is a lazy eye. In this condition you may see double or print may run together.
General Binocular Problems:
When the two eyes fail to work together, eye strain and fatigue can occur. If left untreated, reduced comprehension or avoidance of reading are commonly found.
Visual Perceptual Dysfunction:
This occurs when eye-hand coordination, visual memory, reversals, and other visual perceptual areas are deficient or undeveloped. This results in decreased efficiency in the development of learning.
Inappropriate Visual Development:
When visual skills of infants are not developing appropriately, strabismus and other visual conditions may occur. If treated immediately, the prognosis is excellent.
Closed Head Trauma Syndrome:
As a result of a head injury, visual skills may be lost or deficient. Often double vision, disorientation and other visual problems result, which should be treated as soon as possible.
Bibliography
"Glossary of Common Vision Conditions." VisionHelp..
"Eye Anatomy." Cataract & Laser Institute. St.Lukes. http://www.stlukeseye.com/Anatomy.asp.
"Glossary of Common Vision Conditions." VisionHelp.
"Eye Anatomy." Cataract & Laser Institute. St.Lukes. http://www.stlukeseye.com/Anatomy.asp.
sorry this is so late mr.wirth, i kept having problems with uploading the pictures but i finally figured out how to get it to work!
Chapter 20 Question 63
Between 1880 and 1883 James Wimshurst invented the Wimshurst machine, which is able to generate high voltages. It consists of two insulated disks that rotate in opposite directions. An imbalance of charges is induced, then amplified, then collected by two metal combs.
In 1975, Pieter van Musschenbroek invented the Leyden jar. This was the first capacitor, an electrical device that is able to store energy. This was a sealed glass jar with water in it. There is a wire that runs through the cork and into the water; there is a thin layer of metal coating.
In 1975, Pieter van Musschenbroek invented the Leyden jar. This was the first capacitor, an electrical device that is able to store energy. This was a sealed glass jar with water in it. There is a wire that runs through the cork and into the water; there is a thin layer of metal coating.
Thursday, March 13, 2008
March 13 Class Notes
We went over the homework at the start of class. We then watched a video on electric fields and lines of force. The rest of class was spent working on problem set 2. We also recieved the answers to problem sets 1 & 2.
Leyden Jar
The Leyden jar was invented in 1745 by Pieter van Musschenbroek. It was the first capacitor that was used as a devide for storing electric charge and to conduct early experiments in electricity. A typical design consists of a top electrode electrically connected usually by a chain to a metal foil which coats part of the inner surface of a glass jar. An electrostatic generator charges the jar and is connected to the inner electrode while the outer plate is grounded. Wrapped around the outside of the jar is a conducting foil which matches the internal coated area. The jar has equal but opposite charges in the inner and outer surfaces of the jar. Originally, the device was just a glass bottle that was partially filled with water and had a metal wire passing through a cork closing it. However, it was soon discovered by Watson in 1746 that it was better to coat the exterior of the jar with metal foil. This was better because it left the impure water inside acting as a conductor, connected by a chain to a sphere (external terminal). Initially it was believed that the charge was stored in water and after further investigation by Benjamin Franklin it was concluded that the charge was stored in the glass—not the water. Today we know that the the charge is actually stored in a thin layer along the facing surfaces which touch the glass also known as the dielectric.
Wednesday, March 12, 2008
Chapter 20 Question 63
The Leyden jar was invented in 1745 by Pieter Van Musschenbroek. It was a device for storing an electric charge. The Leyden jar was the first ever capacitor. Leyden jars were mostly used to conduct early experiments in electricity.
The Wimshurst Machine was invented in the late 1800s by James Wimshurst. A Wimshurst Machine is a device for generating a high voltage electric charge. It has two large rotating discs that spin in the opposite direction to the other.
Question 63
The leyden jar was used by early experimenters to store electricity. The leyden jar consisted of an insulator with a layer of metal on the inside and the outside of it. The inside metal is given a charge with the outside metal being grounded. When this occurs the outside metal has an equal but opposite reaction. When the outside and inside metals are connected a spark occurs and both metals are grounded. Scientists today would call a machine like this a capacitator. In Wimshurst design, the disks contra-rotate. The metal foil sectors on the disks induce charges on each other, which are picked off with metal brushes and stored in Leiden jars. The machine was developed to form high voltages in the late 19th century. The positive feedback of the Wimshurst design increases the accumulating charges until the breakdown voltage of the air is reached and a spark jumps across the gap. Both of these designs were very successful during their time in studying static electricity.
The Electrophorus took the place of the Leyden jar and is the two-plate principle that is behind the electrical condensers in use today. Invented in 1775 by Alessandro Volta, its purpose was to create and store an electrostatic charge.
What does it consist of? The electrophorus consists of a dielectric plate (originally a 'cake' of resinous material like pitch or wax, but in modern versions plastic is used) and a metal plate with an insulating handle.
The Van de Graaff generator was invented in 1929 by Robert J. Van de Graaff and is one of the most famous of all the elec
trostatic devices. It uses a conveyor belt to carry an electric charge from a high-voltage supply to a hollow ball. Another generator was modified to produce x-rays to be used in treating internal tumors in Boston in 1927. Van de Graaff's first generator operated at 80,000 volts and eventually would be improved to five million volts. This generator remains one of the most widely used experimental exhibits in schools and museums today.Why did it come about? Van de Graaff needed to accelerate subatomic particles to a very high velocity to test the properties of atoms. He knew that by storing an electrostatic charge, could result in many benefits. -DH
18th & 19th Century Static Electricity Devices
The Layden jar (above) was invented by Pieter van Musschenbroek in 1745 and named after the Universityof Leyden in the Netherlands. The jar was originally a sealed glass jar with a wire running through the cork seal and into the water within the bottle. The bottle had a conuctor wrapped around it. Later the water was replaced by a coating of conducting metal around the inside of the jar. The bottle can store the charge passed in through the wire on the thin layer of conductor around the inside of the jar, which is called a dielectric.
The Aepinus condenser (below) was invented by Franz Aepinus in 1789. Today, condensers are known as capacitors, which store energy between to plates. The condenser was used to demonstrate conduction and induction. It was designed so that the two plates could be moves, and the plate could be replaced with a different material. It was the first condenser created after the Leyden jar. 
Leyden Jar
In 1746, Pieter Van Musschenbroeck invented a small device that could store a large electric charge. He called this device the Leyden Jar and it was used to perform many experiments in electricity during the seventeenth and eighteenth century. The original form of the device was just a glass bottle partially filled with water, with a metal wire passing through a cork closing it. The role of the outer plate was provided by the hand of the experimenter. Soon it was found that it was better to coat the exterior of the jar with metal foil, leaving the impure water inside acting as a conductor, connected by a chain or wire to an external terminal, a sphere, to avoid losses by corona discharge. It was initially believed that the charge was stored in the water. Ben Franklin investigated the Leyden Jar, and concluded that the charge was stored in the glass, not in the water, as others had assumed. (wikipedia)
#63 - Sarah S.
Wimshurst 
Leiden
Leiden
The Leiden Jar
History: 1745 - Ewald Kleist, stored large amounts of electric charge by lining a glass jar with silver foil, and charged the foil with a friction. He received a shock. 1746 - Dutch physicist Pieter van Musschenbroek of the University of Leyden made the same discovery
Consists of: A glass cylindrical container (jar) with an outer and inner metal (foil) coating covering the bottom and sides of an insulator (plastic or glass).
Brass rod with an external knob passing through a wooden stopper that is connected to the inner coating by a loose metal chain.
How it works: an electrical charge is applied to the external knob and positive and negative charges accumulate from the two metal coatings respectively. However, they are unable to discharge due to the glass between them. The result is the charges will hold each other in equilibrium until a discharge path is provided. Charge is stored not in the conductors but in a thin layer along the facing surfaces that touch the glass. When the outside and inside surfaces are connected by a conductor there is a spark and everything is grounded.
Uses: store electricity in experiments and a condenser in early wireless equipment.
The Whimshurst Machine
History: developed between 1880 and 1883 by James Wimshurst
Consists of : with two large contra-rotating discs mounted in a vertical plane, two cross bars with metallic brushes, and a spark gap formed by two metal spheres.
How it works: creates electric charges through electrostatic induction
two insulated disks and their metal sectors rotate in opposite directions, metal foil sectors on the disks induce charges on each other, which are amplified and collected by metal brushes and stored in Leiden jars, spark jumps across gap
machine is self-starting (no external electrical power required to create the initial charge). Does require mechanical power to turn the disks against the electric field (this is the energy that the machine converts into electric power). The output is a current proportional to the area covered by the metal sectors and to the rotation speed.
Becky Salisbury
The Leyden jar was a device invented in Pieter van Musschenbroek in 1745 that was used for storing electric charge. It was one of the earliest inventions used for experiments in electricity. In respect to the design of the Leyden jar, the outer plate was grounded whereas the inner and outer surfaces of the jar stored equal but opposite charges. Benjamin Franklin was actually studying the Leyden jar, and was the first to realize that the charge was actually stored in the glass and not the water inside the jar. The storage ability or capacitance of the Leyden jar is about 1 farad, an SI measuring unit of capacitance. This great invention was one of the first inventions which helped scientist study static electricity.
The Leyden jar was a device invented in Pieter van Musschenbroek in 1745 that was used for storing electric charge. It was one of the earliest inventions used for experiments in electricity. In respect to the design of the Leyden jar, the outer plate was grounded whereas the inner and outer surfaces of the jar stored equal but opposite charges. Benjamin Franklin was actually studying the Leyden jar, and was the first to realize that the charge was actually stored in the glass and not the water inside the jar. The storage ability or capacitance of the Leyden jar is about 1 farad, an SI measuring unit of capacitance. This great invention was one of the first inventions which helped scientist study static electricity.
Tuesday, March 11, 2008
Question 63
Although there were several devices used in the seventeenth and eighteenth centuries to study static electricity, the two most well known were the Leyden jar and the Wimshurst machine. The quest for more knowledge involving static electricity was a theme of these two centuries. First off, the Leyden jar was discovered, accidently, by a Dutch physicist by the name of Pieter van Musschenbroek in 1745. The Leyden jar contained an electrode located at the top that was then connected with some kind of conductor to the inner surface of a glass jar. The charges on the inside and outside differ with whether or not they are positive or negative, but in any case there is an equal amount of them. At first water was used in the inside to be created as a means of travel for the condcutor, but later it was discovered that wrapping the glass with metal foil was a better method.
The Wimshurst machine creates static electric sparks when cranked. It is made of two plastic discs, each with spaced out metal sectors. This machine has to supporters on either side and contains a hand wheel used to crank and operate this piece of science equiptment. It also comes with induced charge collecting enablers and Leyden jar capacitators to help maximize its static electric sparks and effectiveness. The hand crank allows for the sparks to happen.
#63
The Layden Jar is an early device for storing electric charge that was invented in 1745 by Pieter van Musschenbroek. It was the first capacitor. It consisted of a top electrode electrically connected to metal foil coating a glass jar and a brass knob at the end. When an electrical charge is applied to the external knob, positive and negative charges accumulate from the two metal coatings respectively, but are unable to discharge because of the glass between them. The result is that the charges will hold each other in equilibrium until a discharge path is provided. These were first used to store electricity, but were later used as a condenser in early wireless equipment.The Wimshurt machine is as electrostatic device for generating high voltages developed in 1880. It has two large contra-rotating discs mounted in a vertical plane. Their metal sectors rotate in the opposite direction passing the crossed metal. An imbalance in charges is induced, amplified, and collected by two pairs of metal combs. The positive feedback increases until the breakdown voltage of air is reached and a spark jumps across.
History of Science - Leyden Jar
The concept of the leyden jar was invented by the ancient Greeks and then expanded on by a German scientist in 1745. A typical design consists of a top electrode connected, by a chain, to a metal foil, coating part of the inner surface of a glass jar. A conducting foil is wrapped around the outside of the jar. The jar is charged by an electrostatic generator connected to the inner electrode while the outer plate is grounded. The inner and outer surfaces of the jar store equal, but opposite charges. Leyden jars are typically used to build and store electricity and is currently known as a capacitator.
Monday, March 10, 2008
? # 63
Technology was lacking in the seventeenth and eighteenth centuries compared to what is available at our fingertips today. Even so this time period had its share of science innovation. For example, in science there were ways that scientists were able to study static electricity. One of the ways they were able to do so was the Leyden jar. The Leyden jar is constructed with a glass jar that has an electrode attached to a piece of foil inside of it. Plus, there is a conducting foil is wrapped around the outside of the jar, matching the internal coated area. Finally the whole device is completed by charging it with generator. The jar works by holding the charges from the generator as they are equal but opposite.
March 4th Scribe
First we went over the test, then we found out that test corrections were due on the 5th because five week grades were due at that time as well. Then Mr. Wirth asked the question, What do you know about electricity? Their were very few responses, but the class was eager to learn the wonders of electricity. In the beginning of class we did some amber demos. then we used the rubber and glass and rubbed them against silk and fur to see the power of static electricity. This is where we found out that opposites attract and that water attracts to both rubber and glass. Then we learned about the electroscope, and how positives repel each other. Next Mr. Wirth showed us the magic water and how it attracts and repels to different materials. It is important to know that static electricity is not actually static, it is in fact moving. Also, electricity comes from matter. Another important fact to remember is that protons never leave because that would change the atomic number of the atom. Hopefully for anyone that needed a refresher or was not in class, this will be an effective tool.
Sunday, March 9, 2008
03/07/08 What happened?
Some people might be asking themselves, What happened friday? I hope I can answer some of the questions regarding 5th period...the rest is up to you to remember.
The beginning of the class was revolved around checking the homework with the answers up on the overhead. Like many Fridays, it was a pretty talkative group. Conversations about physics related things of course. After about ten minutes or so of homework talk, Mr. Wirth went on to explain the mini-lab that the class was going to work on that day.
***
After the groups returned back to their seats, Mr. Wirth passed out graded work and showed us our weekend homework...
------------------------------------
Read Chapter 20 (p. 540-561)
Do problems: #1, 5, 6, 16, 18, 19, 21
DUE: Tuesday, March 11th*
*Students can either hand write or type up the homework and it will be collected and be graded.
------------------------------------
There is a online version of the textbook located on the physics website in the side tool bar on the homepage if you can't find your own book.
Make sure to know how to use an electroscope, if not be sure to see Mr. Wirth with questions.
That's about it. Enjoy.
-DH
The beginning of the class was revolved around checking the homework with the answers up on the overhead. Like many Fridays, it was a pretty talkative group. Conversations about physics related things of course. After about ten minutes or so of homework talk, Mr. Wirth went on to explain the mini-lab that the class was going to work on that day.
First, Mr. Wirth charges up the ruler with wool, making the ruler negative.
Next he charges the rod with the bunny skin, making the rod negative.
The reaction of two negatively charged objects to each other is <-----> repulsive.
***
After the groups returned back to their seats, Mr. Wirth passed out graded work and showed us our weekend homework...
------------------------------------
Read Chapter 20 (p. 540-561)
Do problems: #1, 5, 6, 16, 18, 19, 21
DUE: Tuesday, March 11th*
*Students can either hand write or type up the homework and it will be collected and be graded.
------------------------------------
There is a online version of the textbook located on the physics website in the side tool bar on the homepage if you can't find your own book.
Make sure to know how to use an electroscope, if not be sure to see Mr. Wirth with questions.
That's about it. Enjoy.
-DH
Wednesday, March 5, 2008
3/5/08 scribe thingy
So today we took a lot of notes….
Today started off somewhat exciting with a four minute video about Benjamin Franklin. Nobody really understood what happened in the video because everyone was playing Frisbee, to be completely honest. We then talked about matter as a source of electricity. Matter is composed of atoms which are composed of neutrons (neutral charge), protons (positive charge), and electrons (negative charge). Neutrons and protons are located in the nucleus of an atom and the electron orbits the nucleus. We finished with matter and went into what a Coulomb is. This is a scalar quantity and 1 Coulomb = 6.25 x 10^18 elementary charges and one elementary charge = 1.60 x 10^-19 C. After that, we figured out the reasoning behind how an object becomes positively or negatively charged. This happens when there is either an excess or a deficiency of electrons. The way an object becomes electrically charged is by gaining or losing electrons which all depends on the tendency of the material. We also did a demo on how to attract a neutral object. Mr. Wirth showed it was possible by rubbing a balloon on his head and then sticking it to the wall and showing us that it would stay where he left it. We then took a look at an electroscope. This is a device that determines the presence of an electrical charge and whether it’s positive or negative. Finally, we learned that there are ways to remove or add electrons to neutralize the static charge which is called grounding. Some examples of this are grounding straps and lightning rods. The End
Monday, March 3, 2008
Optical Fibers
Fiber optics are used to transport light and can allow for communications over long distances at much higher rates. Fibers are used in place of wire because they are not affected by electromagnetic forces.
Optical fibers work due to something known as total internal reflection, they more or less guide waves through the cable. There is a core and an outer layer that make up an optical fiber. The inner layer has a greater refractive index than the outer layer which causes light to reflect back into the inner layer. Due to the way the cables are designed they can not be easily connected in the way that wire can. They most be arched together perfectly in order to work properly.
Optical fibers have many uses in the world today. They are largely used in communications over long distances. This makes the use of repeaters unnecessary due to the fact that light travels through the cables without being lost. They each cable can also carry multiple wavelengths of light at the same time. These cables can save space and time because they can carry more in one cable than a number of other cables combined at much high speeds. They also make wire tapping extremely difficult due to the fact that they can not be easily joined with other cables. Because they are made out of glass or plastic they work by transporting light instead of electrical signals.
Another application for optical fibers is in sound. They can be used in SONAR and hydrophone systems quite easily due to the fact that they do not need electricity. They can also be used in temperature reading because they can operate at much higher temperatures.
Optical fibers are usually made of either glass or plastic. The glass fibers are generally made from silica or other materials depending on the wavelengths of the light that they will be transmitting. The glasses all generally have an index of refraction near 1.5. This gives the difference between the core and outer layer a difference of roughly one percent.
Optical fibers work due to something known as total internal reflection, they more or less guide waves through the cable. There is a core and an outer layer that make up an optical fiber. The inner layer has a greater refractive index than the outer layer which causes light to reflect back into the inner layer. Due to the way the cables are designed they can not be easily connected in the way that wire can. They most be arched together perfectly in order to work properly.
Optical fibers have many uses in the world today. They are largely used in communications over long distances. This makes the use of repeaters unnecessary due to the fact that light travels through the cables without being lost. They each cable can also carry multiple wavelengths of light at the same time. These cables can save space and time because they can carry more in one cable than a number of other cables combined at much high speeds. They also make wire tapping extremely difficult due to the fact that they can not be easily joined with other cables. Because they are made out of glass or plastic they work by transporting light instead of electrical signals.
Another application for optical fibers is in sound. They can be used in SONAR and hydrophone systems quite easily due to the fact that they do not need electricity. They can also be used in temperature reading because they can operate at much higher temperatures.
Optical fibers are usually made of either glass or plastic. The glass fibers are generally made from silica or other materials depending on the wavelengths of the light that they will be transmitting. The glasses all generally have an index of refraction near 1.5. This gives the difference between the core and outer layer a difference of roughly one percent.
The Human Eye
The human eye is a complex organ with a variety of layers and muscles. Obviously, it is used to help humans see. However, many humans experience vision problems that either impair their vision or prevent them from seeing altogether. Approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall, the human eye is composed of fifteen main parts. Below is a detailed image of the eye:
Maintaining the shape of the eye is the tough, outermost layer the sclera. A clear layer, the cornea, covers the front of the sclera. Light first passes through the cornea when it enters the eye. Attached to the sclera are the extraocular muscles that move the eye. The choroid is the second layer of the eye. It contains the blood vessels that supply blood to all structures of the eye. The choroid is composed of the ciliary body and the iris. A muscular area that is attached to the lens, the ciliary body contracts and relaxes to control the size of the lens for focusing. Functioning to color the eye, the iris is an adjustable diaphragm surrounding the pupil. It has two muscles: the dilator and the sphincter. Both control the amount of light let into the eye by adjusting the pupil size. The color of the iris is determined by the color of the connective tissue and pigment cells. The innermost layer is the retina -- the light-sensing portion of the eye. It contains rod cells, which are responsible for vision in low light, and cone cells, which are responsible for color vision and detail. In the back of the eye, in the center of the retina, is the macula. In the center of the macula is an area called the fovea centralis. This area contains only cones and is responsible for seeing fine detail clearly. Inside the eyeball there are two fluid-filled sections separated by the lens, a clear structure used to fine-tune vision. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor. When drainage of the aqueous humor is blocked, a disease called glaucoma can result. The eye is unique in that it is able to move in many directions to maximize the field of vision, yet is protected from injury by a bony cavity called the orbital cavity. The eye is embedded in fat, which provides some cushioning. The eyelids protect the eye by blinking. Eyelashes and eyebrows protect the eye from particles that may injure it.
There are six muscles attached to the sclera that control the movements of the eye. They are shown here with their descriptions:
Muscle
Primary Function
Medial rectus
moves eye towards nose
Lateral rectus
moves eye away from nose
Superior rectus
raises eye
Inferior rectus
lowers eye
Superior oblique
rotates eye
Inferior oblique
rotates eye
After passing through the cornea, light passes through the aqueous humor, lens and vitreous humor. Ultimately it reaches the retina, which is the light-sensing structure of the eye. The retina is made up of cones and rods and is lined with black pigment called melanin to lessen the amount of reflection. The retina has a central area, called the macula that is responsible for sharp, detailed vision. The color-responsive chemicals in the cones are called cone pigments and are very similar to the chemicals in the rods. Each cone cell has a red-sensitive pigment, a green-sensitive pigment, and a blue-sensitive pigment. The presence of these pigments allow the eye to be sensitive to that color. The human eye can sense almost any gradation of color when red, green and blue are mixed.
In the diagram above, the wavelengths of the three types of cones (red, green and blue) are shown. The peak absorbency of blue-sensitive pigment is 445 nanometers, for green-sensitive pigment it is 535 nanometers, and for red-sensitive pigment it is 570 nanometers. Color blindness is the inability to differentiate between different colors. The most common type is red-green color blindness. This occurs in 8 percent of males and 0.4 percent of females. It occurs when either the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. Another vision problem is vitamin A deficiency. When severe vitamin A deficiency is present, then night blindness occurs. This is when the levels of light-sensitive molecules are low due to vitamin A deficiency, there may not be enough light at night to permit vision. During daylight, there is enough light stimulation to produce vision despite low levels of retinal. Refraction is when light rays reach an angulated surface of a different material and the light rays bend. When light reaches a convex lens, the light rays bend toward the center:
When light rays reach a concave lens, the light rays bend away from the center:
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. 20/20 vision means when standing 20 feet away from the chart you can see what a "normal" human being can see and have normal vision. If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. 20/200 is the cutoff for legal blindness in the United States. It is also possible to have vision better than normal. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart. Hawks, owls and other birds of prey have much more acute vision than humans. A hawk has a much smaller eye than a human being but has lots of sensors (cones) packed into that space. This gives a hawk vision that is eight times more acute than a human's. A hawk might have 20/2 vision!
Normally, your eye can focus an image exactly on the retina:
Nearsightedness and farsightedness occur when the focusing is not perfect. When nearsightedness is present, a person can clearly see near objects, while experiencing difficulty seeing far objects. Light rays become focused in front of the retina. This is caused by an eyeball that is too long, or a lens system that has too much power to focus. Nearsightedness is corrected with a concave lens. This lens causes the light to diverge slightly before it reaches the eye, as seen here:
When farsightedness is present, a person can clearly see far objects, but has trouble seeing seeing near objects. Light rays become focused behind the retina. This is caused by an eyeball that is too short, or by a lens system that has too little focusing power. This is corrected with a convex lens, as seen here:
As stated earlier, to be legally blind visual acuity must be less than 20/200 with corrective lenses. Some causes of blindness include cataracts, glaucoma, macular degeneration, trauma, vitamin A deficiency, tumors, strokes, neurological diseases, hereditary diseases and toxins.
The human eye is an interesting organ full of potential complications and great physics lessons. With a complex anatomy and many ways to create problems, its no wonder so many people wear contacts.
Works Cited
Bianco, MD, Dr. Carl. "How Vision Works." How Stuff Works. 2008. 15 Feb 2008.
Maintaining the shape of the eye is the tough, outermost layer the sclera. A clear layer, the cornea, covers the front of the sclera. Light first passes through the cornea when it enters the eye. Attached to the sclera are the extraocular muscles that move the eye. The choroid is the second layer of the eye. It contains the blood vessels that supply blood to all structures of the eye. The choroid is composed of the ciliary body and the iris. A muscular area that is attached to the lens, the ciliary body contracts and relaxes to control the size of the lens for focusing. Functioning to color the eye, the iris is an adjustable diaphragm surrounding the pupil. It has two muscles: the dilator and the sphincter. Both control the amount of light let into the eye by adjusting the pupil size. The color of the iris is determined by the color of the connective tissue and pigment cells. The innermost layer is the retina -- the light-sensing portion of the eye. It contains rod cells, which are responsible for vision in low light, and cone cells, which are responsible for color vision and detail. In the back of the eye, in the center of the retina, is the macula. In the center of the macula is an area called the fovea centralis. This area contains only cones and is responsible for seeing fine detail clearly. Inside the eyeball there are two fluid-filled sections separated by the lens, a clear structure used to fine-tune vision. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor. When drainage of the aqueous humor is blocked, a disease called glaucoma can result. The eye is unique in that it is able to move in many directions to maximize the field of vision, yet is protected from injury by a bony cavity called the orbital cavity. The eye is embedded in fat, which provides some cushioning. The eyelids protect the eye by blinking. Eyelashes and eyebrows protect the eye from particles that may injure it.
There are six muscles attached to the sclera that control the movements of the eye. They are shown here with their descriptions:
Muscle
Primary Function
Medial rectus
moves eye towards nose
Lateral rectus
moves eye away from nose
Superior rectus
raises eye
Inferior rectus
lowers eye
Superior oblique
rotates eye
Inferior oblique
rotates eye
After passing through the cornea, light passes through the aqueous humor, lens and vitreous humor. Ultimately it reaches the retina, which is the light-sensing structure of the eye. The retina is made up of cones and rods and is lined with black pigment called melanin to lessen the amount of reflection. The retina has a central area, called the macula that is responsible for sharp, detailed vision. The color-responsive chemicals in the cones are called cone pigments and are very similar to the chemicals in the rods. Each cone cell has a red-sensitive pigment, a green-sensitive pigment, and a blue-sensitive pigment. The presence of these pigments allow the eye to be sensitive to that color. The human eye can sense almost any gradation of color when red, green and blue are mixed.
In the diagram above, the wavelengths of the three types of cones (red, green and blue) are shown. The peak absorbency of blue-sensitive pigment is 445 nanometers, for green-sensitive pigment it is 535 nanometers, and for red-sensitive pigment it is 570 nanometers. Color blindness is the inability to differentiate between different colors. The most common type is red-green color blindness. This occurs in 8 percent of males and 0.4 percent of females. It occurs when either the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. Another vision problem is vitamin A deficiency. When severe vitamin A deficiency is present, then night blindness occurs. This is when the levels of light-sensitive molecules are low due to vitamin A deficiency, there may not be enough light at night to permit vision. During daylight, there is enough light stimulation to produce vision despite low levels of retinal. Refraction is when light rays reach an angulated surface of a different material and the light rays bend. When light reaches a convex lens, the light rays bend toward the center:
When light rays reach a concave lens, the light rays bend away from the center:
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. 20/20 vision means when standing 20 feet away from the chart you can see what a "normal" human being can see and have normal vision. If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. 20/200 is the cutoff for legal blindness in the United States. It is also possible to have vision better than normal. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart. Hawks, owls and other birds of prey have much more acute vision than humans. A hawk has a much smaller eye than a human being but has lots of sensors (cones) packed into that space. This gives a hawk vision that is eight times more acute than a human's. A hawk might have 20/2 vision!
Normally, your eye can focus an image exactly on the retina:
Nearsightedness and farsightedness occur when the focusing is not perfect. When nearsightedness is present, a person can clearly see near objects, while experiencing difficulty seeing far objects. Light rays become focused in front of the retina. This is caused by an eyeball that is too long, or a lens system that has too much power to focus. Nearsightedness is corrected with a concave lens. This lens causes the light to diverge slightly before it reaches the eye, as seen here:
When farsightedness is present, a person can clearly see far objects, but has trouble seeing seeing near objects. Light rays become focused behind the retina. This is caused by an eyeball that is too short, or by a lens system that has too little focusing power. This is corrected with a convex lens, as seen here:
As stated earlier, to be legally blind visual acuity must be less than 20/200 with corrective lenses. Some causes of blindness include cataracts, glaucoma, macular degeneration, trauma, vitamin A deficiency, tumors, strokes, neurological diseases, hereditary diseases and toxins.
The human eye is an interesting organ full of potential complications and great physics lessons. With a complex anatomy and many ways to create problems, its no wonder so many people wear contacts.
Works Cited
Bianco, MD, Dr. Carl. "How Vision Works." How Stuff Works. 2008. 15 Feb 2008
Sunday, March 2, 2008
Lucien's blog
Lucien Rouse
Mr. Wirth
Regents Physics
2 March 2, 2008
Light’s Behavior in the Sky
We all know that a beam of light is typically white. So why then, does the sky appear blue when there is only atmosphere between the sun and us, and, even more confusing, is why does the sky change colors during the sunset? How do rainbows materialize when the sun reappears after a shower? Lastly, what causes mirages, a trick of the mind, or something more realistic? Simple wave characteristics can be used to explain all of these phenomena.
When a child asks why the sky is blue, we typically answer that, “it just is.” What the child really should be told is that it is because of earth’s atmosphere. Earths atmosphere is made up of roughly seventy eight percent nitrogen, twenty one percent oxygen, and about one percent of other various gases; most prevalent among them is argon. Although the atmosphere seems invisible to the human eye, it actually absorbs about sixty percent of visible light. Here is where it gets back to the color of the sky. When solar radiation from the sun strikes the atmosphere, waves with a lower wavelength get absorbed. So particles in the atmosphere absorb the lower wavelength blue waves and the higher wavelength red waves pass through. The low wavelength waves are absorbed by the gas molecules in the atmosphere, then scattered. So the blue light is scattered, in all directions and whenever we look up, the sky appears blue. For the same reason, the horizon appears lighter. The blue light travels further, and passes through even more atmospheric particles, and is thus scattered ever more. Rayleigh scattering, as well as Mie Theory, explains the phenomena perfectly.
http://www.sciencemadesimple.com/sky_blue.html
At sunset, the sky appears red because the sun is almost tangent to the earth’s surface. Blue wavelengths are still scattered, but the light has to travel further to reach you, so even more of it is scattered, and only red light reaches you directly, so the sun appears less bright, and more red. The sky around it changes colors if there are a lot of water or dust particles in the air. They reflect the sun’s light in all different directions, and again, the blue light is scattered, so red light reaches the observer.
http://www.sciencemadesimple.com/sky_blue.html
The next question is about how rainbows are formed. The answer has to do with water particles in the air, and how light reacts to them. When white light hits a water particle, it is refracted and dispersed at entry, reflected by the back of the water particle, and refracted a second time when exiting. The result is that the different wavelengths of light are spread out, forming the red, orange, yellow, green, blue, indigo, and violet arc.
http://en.wikipedia.org/wiki/Rainbow
No matter what part of the rainbow you look at, that part of the rainbow is at forty-two degrees from your horizontal viewpoint and that part of the rainbow. This is because the light ray is refracted twice and reflected once, so the rainbow exits the droplet at a one hundred and thirty eight degree difference than it’s starting direction. One hundred and eighty minus one hundred and thirty eight equals forty-two, so the resulting rainbow that we see is always forty-two degrees off of lights direct path towards us.
The last question is about mirages. The typical thinking is that it is the delusional hallucination of dehydrated travelers, but in reality, anyone can see a mirage. Mirages occur when there is a severe difference in the temperature of different mediums that light pass through. For example, the ground near a road is often much warmer than the air above it. Light travels slower through warmer air, so, therefore, when light travels from cold air to warmer air, it will refract away from the temperature gradient. This is called an inferior image, and it is the type of mirage that makes the sky appear to be on the ground.
http://en.wikipedia.org/wiki/Mirage
By contrast, when light goes from hot air to cold air, a superior image is produced. These mirages are more complicated (they can be upside down or right side up) but they are basically the result of light being bent towards the temperature gradient, and then going through other stages. Superior images are only interesting because of the earth’s spherical shape, and they are what allow islands to appear closer to the shore than they really are. Mirages can only occur when the temperature difference is at least two degrees Celsius, but they are most clear with about a four and a half degree Celsius difference. Mirages are real enough even to be photographed.
Despite the common answers to these even more common questions, each of these phenomena is a result of light waves and the mediums that it travels through. It all has to do with wave characteristics, the very same ones that we are studying in Physics right now.
Work Cited
"About Rainbows." Aug. 2005. University Corperation for Atmospheric Reseach. 2 Mar. 2008.
"Why is the Sky Blue?" Science Made Symple. 1997. 2 Mar. 2008. Young, Andrew T. "An Introduction to Mirages." 1999. 2 Mar. 2008 .
Mr. Wirth
Regents Physics
2 March 2, 2008
Light’s Behavior in the Sky
We all know that a beam of light is typically white. So why then, does the sky appear blue when there is only atmosphere between the sun and us, and, even more confusing, is why does the sky change colors during the sunset? How do rainbows materialize when the sun reappears after a shower? Lastly, what causes mirages, a trick of the mind, or something more realistic? Simple wave characteristics can be used to explain all of these phenomena.
When a child asks why the sky is blue, we typically answer that, “it just is.” What the child really should be told is that it is because of earth’s atmosphere. Earths atmosphere is made up of roughly seventy eight percent nitrogen, twenty one percent oxygen, and about one percent of other various gases; most prevalent among them is argon. Although the atmosphere seems invisible to the human eye, it actually absorbs about sixty percent of visible light. Here is where it gets back to the color of the sky. When solar radiation from the sun strikes the atmosphere, waves with a lower wavelength get absorbed. So particles in the atmosphere absorb the lower wavelength blue waves and the higher wavelength red waves pass through. The low wavelength waves are absorbed by the gas molecules in the atmosphere, then scattered. So the blue light is scattered, in all directions and whenever we look up, the sky appears blue. For the same reason, the horizon appears lighter. The blue light travels further, and passes through even more atmospheric particles, and is thus scattered ever more. Rayleigh scattering, as well as Mie Theory, explains the phenomena perfectly.
http://www.sciencemadesimple.com/sky_blue.html
At sunset, the sky appears red because the sun is almost tangent to the earth’s surface. Blue wavelengths are still scattered, but the light has to travel further to reach you, so even more of it is scattered, and only red light reaches you directly, so the sun appears less bright, and more red. The sky around it changes colors if there are a lot of water or dust particles in the air. They reflect the sun’s light in all different directions, and again, the blue light is scattered, so red light reaches the observer.
http://www.sciencemadesimple.com/sky_blue.html
The next question is about how rainbows are formed. The answer has to do with water particles in the air, and how light reacts to them. When white light hits a water particle, it is refracted and dispersed at entry, reflected by the back of the water particle, and refracted a second time when exiting. The result is that the different wavelengths of light are spread out, forming the red, orange, yellow, green, blue, indigo, and violet arc.
http://en.wikipedia.org/wiki/Rainbow
No matter what part of the rainbow you look at, that part of the rainbow is at forty-two degrees from your horizontal viewpoint and that part of the rainbow. This is because the light ray is refracted twice and reflected once, so the rainbow exits the droplet at a one hundred and thirty eight degree difference than it’s starting direction. One hundred and eighty minus one hundred and thirty eight equals forty-two, so the resulting rainbow that we see is always forty-two degrees off of lights direct path towards us.
The last question is about mirages. The typical thinking is that it is the delusional hallucination of dehydrated travelers, but in reality, anyone can see a mirage. Mirages occur when there is a severe difference in the temperature of different mediums that light pass through. For example, the ground near a road is often much warmer than the air above it. Light travels slower through warmer air, so, therefore, when light travels from cold air to warmer air, it will refract away from the temperature gradient. This is called an inferior image, and it is the type of mirage that makes the sky appear to be on the ground.
http://en.wikipedia.org/wiki/Mirage
By contrast, when light goes from hot air to cold air, a superior image is produced. These mirages are more complicated (they can be upside down or right side up) but they are basically the result of light being bent towards the temperature gradient, and then going through other stages. Superior images are only interesting because of the earth’s spherical shape, and they are what allow islands to appear closer to the shore than they really are. Mirages can only occur when the temperature difference is at least two degrees Celsius, but they are most clear with about a four and a half degree Celsius difference. Mirages are real enough even to be photographed.
Despite the common answers to these even more common questions, each of these phenomena is a result of light waves and the mediums that it travels through. It all has to do with wave characteristics, the very same ones that we are studying in Physics right now.
Work Cited
"About Rainbows." Aug. 2005. University Corperation for Atmospheric Reseach. 2 Mar. 2008
"Why is the Sky Blue?" Science Made Symple. 1997. 2 Mar. 2008
Mirages
A mirage is a naturally-occurring optical phenomenon, in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin mirare, meaning 'to appear, to seem'. This is the same root as for mirror. Like a mirror, a mirage shows images of things which are elsewhere. The principal physical cause of a mirage, however, is refraction rather than reflection. A mirage is not an optical illusion. It is a real phenomenon, and one can take photographs of it. The interpretation of the image, however, is up to the fantasy of the human mind.
Mirages occur when there is a rapid shift in air density in the atmosphere -- when the air at one level is a lot hotter than the air at an adjoining level.
This commonly occurs on summer days, when an asphalt road that has been baking in the sun heats the air directly above it, creating a sharp shift in air density levels near the ground. As light passes between the different levels, it bends, creating mirages. Normally, sunlight bouncing off an object (let's say a car) reflects in all directions. You see the car when your eyes detect this light. On an overcast day, you only see the light that bounces off the car straight toward you. This is how you see things most of the time.
On a sunnier day, the light heading straight toward you acts just like it usually does -- it doesn't move through different layers of air density, so it doesn't bend much. But some of the light that would normally hit the ground actually bends in midair because it moves from the cooler, denser air level into the hotter, less dense air right above the ground. As you can see in the diagram below, this produces an interesting effect.
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The lower part of the light wave passes between the layers first, so it speeds up an instant before the upper part. The light that would ordinarily go straight to the ground bends upward and travels to your eyes. The effect is that you see the image of the car twice: once on top of the road, and once in the road surface. The light from the lower part of the car bends farther upward than the light from the top of the car, so the mirage image looks like a reflection. Your brain assumes that the light is traveling in a straight line, so it seems like there's a mirror image beneath the normal image. This mirage looks just like a puddle of water on the road because, like a puddle of water, it's reflecting what's above it. This sort of mirage is called an inferior mirage because it appears below the horizon.
Superior mirages are mirages that form above the horizon. This occurs when there is a cooler level of air lower than a warmer level of air, typically over icy landscapes or very cold water. This mirage causes you to see a scene much higher than it should be. For example, you might see a mass of land or a boat floating in midair. This situation might also distort images, making a boat seem much taller than it actually is.
Bibliography
http://mintaka.sdsu.edu/GF/mirages/mirintro.htmlhttp://www.islandnet.com/~see/weather/elements/supmrge.htm
http://www.sas.org/tcs/weeklyIssues/2004-09-10/gallery/index.html
Physics Explained, Rainbows, Mirages, Color of the Sky and Sunset
The Color of the Sky and Sunset:
In case you were ever one of countless people who have ever wondered to themselves why the sky was blue, then your answer will hopefully be cleared up. It all begins with the simple and complicated physics of it all. To commence understanding, first you must know that whenever any kind of light comes into contact with some sort of boundary between two transparent pieces of material, with different indices of refraction, a portion of this original light is reflected. On the other hand, a portion of its original light is also transmitted due to refraction.
The rainbow occurs because after raining, the droplets of water in the air act as their own tiny prisms, refracted and dispersing the wavelengths of light. As the sunlight goes into the water it reflects and disperses, and depending on the angle of refraction, shows a color in the rainbow. The colors vary due to the angle of refraction and the length of the wavelength. (http://www.howstuffworks.com/question41.htm)
http://inspirationalrainbows.com/images/desert_rainbow.jpg
Lastly, although many may believe they are the mind playing tricks on people, that is actually false. They truly do occur due to the refraction of light in the atmosphere and the changes in air temperature combined with the light. (http://mintaka.sdsu.edu/GF/mirages/mirintro.html)
In case you were ever one of countless people who have ever wondered to themselves why the sky was blue, then your answer will hopefully be cleared up. It all begins with the simple and complicated physics of it all. To commence understanding, first you must know that whenever any kind of light comes into contact with some sort of boundary between two transparent pieces of material, with different indices of refraction, a portion of this original light is reflected. On the other hand, a portion of its original light is also transmitted due to refraction.
To further understand this concept, the picture above shows the line (indicating the boundary) and the two spaces on either side as the transparent material. It then shows the types of reflection, absorption, and the path of light throughout its journey.
You may be wondering what any of this has to do with the answer to why the sky is blue. The previous information shows how the light gets used, some of it reflected, some refracted, some absorbed, and so on. Technically, the sky is blue “simply” because of scattered sunlight. Although we may see the sky as blue, in reality it is more on the violet end of the spectrum but the human eye is not as sensitive to see this. (Patterns in Nature) Continuing to look at the color of the sky, some people might wonder why we see more towards the blue end of the spectrum rather than the red. The answer to this question is that the blue and violet wavelengths are much shorter than red scattering. The idea that the sky was blue because of gases in the atmosphere also was brought up by a scientist named Rayleigh. There have been several theories tested and thought up of by previous experimenters to explain the idea of why the sky was blue.
The scattering of light in an atmosphere is a very important aspect to look at when asking the infamous question of why the sky is blue. Before, the visible spectrum of red and blue was discussed in relation to the color in the sky.1/lambda to the fourth power is the formula used to equate to the scattering of light by molecules.This makes sense because the red end of the spectrum has longer wave lengths than the blue and violet end. If you were to plug a longer wavelength into the formula, you would notice that it would be a much larger number under one, meaning a smaller number as a whole. When a shorter wavelength is plugged in, a smaller more manageable number is created. The atmosphere has a lot to do with the scattering of light. When the sun is at his highest point, or around midday 12 o’clock, it has to pass through the thinnest layer or atmosphere that it has all day. This explains why the sky tends to be brightest and clearer than any other point in the day; and also why you get sunburned or tanned more (since the sun is passing through the thinnest layer of atmosphere.)
This picture and all of the above information after Patterns in Nature was used fromPolarization; and The Human Eye.Again, the wavelengths are a huge part in why we see the sky as blue. The longer wavelengths of the reds and oranges tend to pass straight through, without being changed. The blues and violets are some what tampered with because the shorter wavelengths are far easier to be absorbed. When they are absorbed, they are then radiated and scattered into all different directions. Since the blue light shows up in all directions, you see the whole sky as being blue as a whole, rather than separate parts. For a moment, picture yourself at a beach; when you look out at the clear refreshing blue sky, you notice further out on the horizon there is a paler blue and then almost whitish color. Although this may never have been a mind-boggling thing to you, some people have also pondered this question as much as why the sky was blue. Since the horizon is much farther away from you, there needs to be more blue light at stronger amounts of it to reach you so that you see the same color closer up. However, this is not the case so you see a much lighter version of the blue color you see straight above you. (Blue Sky http://www.sciencemadesimple.com/sky_blue.html)
All of this wavelength information can also be used to help determine why the sunset ends up being red. The longer wavelengths in the early morning and late at night help to explain why the colors red and orange are more apt to show up. The sun goes down and has to go through a thicker atmosphere and therefore the longer wavelengths tend to be way more prominent. The light also must go farther to get to your visible eye while the sun rises and sets because it is on the horizon, rather than right above you. As I said before with the paler and lighter blues on the horizon, the sunrise and sunset is also on the horizon, so the longer wavelengths will get to you easier than the shorter blues and violet wavelengths. That is why you see the reds, oranges, and pinks when the sun sets and rises
http://members.aol.com/danglick01/Sunset1.jpg
Rainbows:
First, to understand rainbows, you must know that white light contains all of the colors of the visible pattern, or as we all know it, “ROYGBIV”. We are able to see these colors lets say, through a prism, because each color has its own wavelength that directs how it bends away, towards, or in any direction. For example, blue light typically refracts because of its shorter wavelength where as green refracts, but less than blue and so on. So when light is shown through a glass prism and it hits at just the right angle, the colors are refracted and dispersed, or scattered about to create the visible spectrum. Also, to create another visual, if sunlight was shown into a glass of water, the light would refract and bend and create a spectrum on the floor where you would see a column of your visible colors. (http://acept.la.asu.edu/PiN/rdg/rainbow/rainbow.shtml#top)
The rainbow occurs because after raining, the droplets of water in the air act as their own tiny prisms, refracted and dispersing the wavelengths of light. As the sunlight goes into the water it reflects and disperses, and depending on the angle of refraction, shows a color in the rainbow. The colors vary due to the angle of refraction and the length of the wavelength. (http://www.howstuffworks.com/question41.htm)
http://inspirationalrainbows.com/images/desert_rainbow.jpg
Mirages:
For many centuries, there have been stories of mirages where people claim to see things that in reality aren’t there, no matter how convinced they are. These “mirages” are created by two layers of air at quite different temperatures. As discussed earlier, when there is a boundary between two transparent materials, light is refracted and reflected. Mirages occur because when the air is at the ground, but not quite touching it, and becomes overheated, an image occurs. I’m sure at one point or another you have been able to see the heat in the air on the ground on a hot summer’s day. There is almost like a ripple effect where it looks like the air is bending and takes on wave like characteristics. (
http://www.unmuseum.mus.pa.us/mirage.htm)For many centuries, there have been stories of mirages where people claim to see things that in reality aren’t there, no matter how convinced they are. These “mirages” are created by two layers of air at quite different temperatures. As discussed earlier, when there is a boundary between two transparent materials, light is refracted and reflected. Mirages occur because when the air is at the ground, but not quite touching it, and becomes overheated, an image occurs. I’m sure at one point or another you have been able to see the heat in the air on the ground on a hot summer’s day. There is almost like a ripple effect where it looks like the air is bending and takes on wave like characteristics. (
Lastly, although many may believe they are the mind playing tricks on people, that is actually false. They truly do occur due to the refraction of light in the atmosphere and the changes in air temperature combined with the light. (http://mintaka.sdsu.edu/GF/mirages/mirintro.html)
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