Waves

Waves
  • Definition: waves are a wiggle in both space in time
    • waves are used so often (ie radio etc.) because waves are a way of sending information without sending matter
  • Antinodes--points throughout medium which oscillate between a large positive displacement and a large negative displacement (maximum vibration)
  • Nodes--points of no displacement; where the wave move least or doesn't move at all (minimum vibration)
  • external image wave_props.gifTrough--depression in a wave
  • Crest--the peak of the wave
  • Medium--the a material which carries a wave
  • Period-- the Time it takes for the wave to come back to the crest
  • Wave length-- the distance between each crest

  • Altitude-- the distance from the equilibrium point of the medium to the farthest point it travels to.
Cool Link​:
To a three-dimensional wave with notes below http://id.mind.net/~zona/mstm/physics/waves/wave3d1/wave3d1.htm


Types of Waves:

Mechanical Waves: Require a material medium to travel; 3 different types

1. Transverse Waves
The medium moves perpendicular to the direction of the wave (ex: light)
Twave.gif
2. Longitudinal Waves
The medium moves parallel to the direction of the wave (ex: sound)
Envision a compressing slinky
Lwave.gif

3. Standing Waves
The transverse and longitudinal waves mixed into one medium
water.gif
This ^ is an example of a water wave.
"A water wave involves a combination of both longitudinal and transverse waves. As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases. The animation above shows a water wave travelling from left to right in a region where the depth of the water is greater than the wavelength of the waves. Two particles are identified in blue to show that each particle indeed travels in a clockwise circle as the wave passes."

Electromagnetic Waves: Don’t require a medium to travel (light, radio)
Matter Waves: Produced by electrons and particles

COLLIDING WAVES

Two waves travelling in opposite directions on the same medium collide:
The amplitude of the resulting wave is the sum of the amplitude of the two original waves
^This^ is called interference.
Constructive interference: the amplitudes of the initial waves are in the same diction so the resulting wave's amplitude is larger than the original waves. The highest point of a constructive interference wave is where the antinode is located (see above for definition, see directly below for image)
csontr.gifwaveadd2.gif
Destructive interference: The amplitudes of the initial waves are in opposite directions so the resulting wave will be zero. The point in the middle of a destructive interference wave is called a node (see above for definition, see directly above for image)

Swinging Pendulum
Sine Function: S = A sin (Bt + C) + D
  • What do A, B, C, and D stand for?
Position Equation for a Pendulum: s = A sin(external image omega.gif t+external image phi.gif) + D

A: AMPLITUDE
  • Change in height of the curve
  • INCREASE A – taller
  • DECREASE A – shorter
external image Wave.png
  • the amplitude is the distance between the equilibrium point*----* and the highest or lowest peak on the graph (check image above)

B : external image omega.gif (omega) ANGULAR FREQUENCY
  • Units = Radians/Second
  • Squishiness changes (peaks either become closer or farther away)
  • INCREASE B – skinner
  • DECREASE B – wider
B_equation.JPG

  • B must be something related to T (Period), but it is not T because T is measured in seconds
  • It could be frequency, # of cycles/ seconds
  • Symbol of frequency à f
  • f = 1 / T
  • Units of frequency à 1 / sec. = Hertz [Hz]
  • My period = 1.49 sec.
  • f = 1 / 1.49 --> f = .67
  • f doesn’t equal my B value, so B cannot be frequency
  • B / f = 6.27 = 2π
  • B / f = 2π
  • B is how fast the pendulum goes through angles à angular frequency
  • B = w = 2π f
  • w = 2π f
B_graph.JPG


C external image phi.gif(phase)
  • C is PHASE (point at which bob is in its cycle)
    • one full cycle is 360 degrees = 2π rad.
  • Units --> radians
  • Horizontal shift (left/right)
  • INCREASE C – left
  • DECREASE C – right

Radians
  • A circle is like a cycle
radian_clock.JPG
Insert Images and Files
Insert Images and Files



  • 360 degrees / 2π rad. = x degrees / 1 rad.
  • 360 degrees = 2π x
  • x = 57
  • 1 radian = 57 degrees
C_graph.JPG


D: VERTICLE SHIFT
  • Vertical shift (up/down)
  • INCREASE D – up
  • DECREASE D – down
  • Units à meters
  • the vertical shift is the distance between the equilibrium point* and the reference point on the graph (for the graph above, 0 on the y axis is the reference point)

  • Not really vertical distance
  • Distance between the bob at equilibrium and the sonic ranger
  • Affects the height of the graph
  • Affects the y intercept
D_graph.JPG

Webassign - Pendulum 02 -- #5

page1final.JPG

STEP 1:

page2final.JPG
Period is the amount of time for a pendulum to go through one cycle. We know that one cycle is from A to C, C to E, or B to D.

STEP 2:
page3final.JPG

Since we are trying to find period, we are dealing with time. This graph plots position vs. time (time on the x axis); therefore, we will use the x axis values of points to find the period. We are going to use points A and C to find the period (although C and E and B and D would work as well). You know the x values of A and C: A is .111 and C is .135. You take the value of C and subtract from it the value of A, leaving you .024 seconds, or the period of the motion.

STEP 3:
page4final.JPG

Amplitude is the distance from the equilibrium point to the peak (equilibrium point to A or equilibrium point to B).

STEP 4:
page5final.JPG


Since we are now dealing with amplitude, we are using values of position. Since this graph plots position vs. time, we are using y axis data. In order to find amplitude you need to find the distance between your two points, in our case A and B. You take the y values of A and B and subtract to find .222. .222 is the whole distance from A to B and we are trying to find the distance from the equilibrium point to either A or B, so we must divide .222 by 2. You find that the amplitude of the motion is .111 meters.

STEP 5:
page6final.JPG

W is the symbol for angular frequency. Angular frequency is how fast a pendulum goes through angles.


STEP 6:
page7final.JPG
In order to find w, you must know the two equations that are related to w: f = 1/T and w=2πf. So far, the only known variable is T (Period: .024 seconds). You can use the first equation to find the value of f. You can use the value of f to then find w in the second equation. You find that w is 261.82 rad/sec.

STEP 7:
page8final.JPG

D is the symbol for vertical shift which is the distance between the bob at the equilibrium point and the sonic ranger.

STEP 8:
page9final.JPG
Since this is the most difficult part of the problem, I have made an example in order to show the steps to find D.

STEP 9:
page10final.JPG


You follow the same steps as in my example above. In order to find the vertical shift (basically the y value of the equilibrium point), you must find the distance between the y values of A and B, .222. You take this number and divide by 2 in order to find the distance from the equilibrium point to either A or B, .111 (our amplitude). In order to find vertical shift, you must add the amplitude (.111) to the y value of B (.666). You will find that the vertical shift is .777 meters.


Sound Waves:

-caused by vibrations
-amplitude=louder or softer
-frequency=pitch of notes
-the higher the amplitude, the louder the sound
-the higher the frequency, the higher pitch of the note

Graphs:
FFT Graph: Fast Fourier Transform
-The high bars are the frequency that you hear the most
-The small bars in other places prove that one note has more than one frequency, but just has one dominant frequency
-Amplitude vs. Frequency (Amplitude: y-axis; Frequency: x-axis)

Position, Velocity, Acceleration, Force, or Energy of a wave vs. Time Graph:
-All sine graphs
-Can determine period, frequency, and amplitude of period
-All look similar
-All have to do with waves

physics.png
These are example graphs for Sound Pressure vs. Time and for an FFT graph.

Visual Sound Waves Video:


This video shows little styrofoam beads changing their motion/vibration back and forth when the frequency changes (sound waves change-- a different note is played). This was found in an art museum and is a good visual to see what really happens when you change the frequency of the sound waves. We always get to hear the waves, but rarely do we get to see it like this.


Here is a cool video about how fire can show different sounds waves with different frequencies by using fire:
In the beginning, the fire is sitting on the tube. Then, as as the man turns on the speakers with 449 Hz, the fire makes a Sin curve that has describes " represents sound".
As the man changes the frequency levels, you can see how the curve changes right when the frequency changes. When the frequency is higher then the fire makes more waves. When the frequency is lower then the fire makes less waves. When he turns on real music with lyrics and instruments, you can see how as each different song comes on, the fire shows how the frequences of souds are constanly changing.

Fun Video about waves/fire:

This video is very fun for understanding waves. Although it is not completely directed to what were studying about waves, it has to do with sound waves/musical notes and their affect on fire. It is considered a 'classic physics experiment' and is fun to watch! You can see how the frequencies change when the note is changed and how that affects the height of the flames.

Speed of Sound Lab
Purpose- find the speed of sound in the air in this room (our classroom)

-We used a microphone, thermostat, lab pro, big tube, and loggerpro. We attached all of these things and snapped our fingers in the tube. The microphone heard the sound waves of the snap and the echo, second echo, and so on that the tube produced.

-Distance= 2 * the height of the tube because the sound waves of the echo had to go down and then back up to the microphone at the top of the tube. In our case the height was 1.324 m.
-Delta T (Change in T) was found on LoggerPro from highlighting the distance from the beginning of the snap to the beginning of the first echo. In our case the delta T was .0079244 s.
-We used the basic equation of s=vt
-Working equation: v= s/t
-V= 2.648 m/.0079244 s
-V= 334.16 m/s
-This was very close to the typical speed of sound which is 343 m/s

-We then used the basic equation of (Vsound= 331.3 m/s + (0.6 m/degreesC*s)(T))
-In our case T (teperature- celcius) = 24.3 degrees celcius
-When we put the values into the equation, we found that the velocity of sound was 345.88 m/s.
-345.88 m/s is the theoretical or actual value

-After finding the theoretical value and the measured value we found the percent error.
-absolute value of actual value (345.88 m/s) - measured value (334.16 m/s) divided by actual value (345.88 m/s) times 100
-When we calculated this out we found it to be 3.39% error!
-Sources of error: clicking in LoggerPro and measuring wrong

-These are just sample numbers, not all numbers will work out this way but these equations can be used with any numbers to find the speed of sound.

-Things that matter when finding speed of sound: air that it is traveling through (or lack there of) and temperature of the air

physics2.png
A graph of the Speed of Sound (Sound Pressure vs. Time)


Biology of Ear
-Outer Ear: focus sound waves due to shape
-Middle Ear: transfer waves from air to fluid-membrane waves
-Inner Ear: help you balance and to transfer the sound to your brain
Major Parts in each part of the Ear:
Middle: ear drum^, hammer*^, anvil*^, stirrup*^
Inner: cochlea, canals, Vestibular nerve (brain nerve)
Hair cells^
*these are the smallest bones in your body
^the parts of the ear that vibrate due to sound waves

physics3.gif
Here is a cool video about how sound goes through the ear and the information goes into the brain:

This video shows how the sound goes into the ear. Then the sound wave's pressure goes into the the ear and hits the ear dream. Then it goes through the rest of ear parts and the information goes to the brain which then the person will know what the sound is and where it is coming from.

The Doppler Effect:
--a change in perceived frequency and wavelength due to the motion of a wave source--
Overall this just means that depending on where you stand relative to a moving object that is making noise, the frequency will change...
external image u10l3d3.gif
The image above shows a girl behind the car and a boy infront of the car (hopefully he will move before something bad happens!). The girl in the image would here a much lower sound due to the lower frequency and the boy would here a much higher pitch even though the siren is still blaring the same sound.
doppler1.gif
http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html


The video above shows a non-moving source producing a steady sound wave pattern - waves which are produced at a constant frequency. Since the source is not moving, the waves propagating from it are symetrical, meaing that there is an equal distance between each ring.
doppler2.gif
http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html

The video above is similar to the first video, however, the source of the sound waves is moving slowly to the right. The source is still producing the waves at a constant frequency, but since the object is moving in one direction, the frequency of the waves change, depending where the rings are in relation to the source. In the video, you can see that the rings infront of the source start to bunch up and get smaller as the source moves. On the opposite side of the source, the rings begin to spread out more and get bigger. The frequency of the waves infront of the source become higher and the frequency of the waves behind the source gets lower. A good example where you could experience this is demonstrated in the example above: if you are in front of a car honking its horn, you will hear a higher pitched sound, but from behind, the sound you hear is lower because of the difference in frequencies.
doppler4.gif
http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html

The video above shows a sound sorce moving at Mach 1 (about the sped of sound, approx 340 m/s of 780 mph). When a source travels at Mach 1, the waves infront of the source bunch up, creating an enormous amount of pressure. This is because the source is only traveling at the speed of sound and has not quite broken the sound barrier. The pressure build-up infront of the source creates a shock wave. This is because the frequencies infront fo the source are so close together that when it passes you, there is just a sort of thump that you hear twhne the source passes you. The source is still traveling on the waves and is not quite infront of them, showing that it is still only at Mach 1.
doppler5.gif
http://paws.kettering.edu/~drussell/Demos/doppler/doppler.html

The video above shows a source moving faster than the speed of sound, a Mach greater than Mach 1. The source is moving faster than the waves it creates and its therefore, in front of the waves. Since it is traveling faster than the speed of sound, to someone observing this, the source will pass them before it actually hears it. Infront of the source, there is still a very intense build-up of pressure, due to the fact that it is moving faster than the speed of sound. A source moving above Mach 1 creates a sonic boom, a supersonic shock wave. This sonic boom travels at the speed of sound and to the observer, there is, well, a BOOM!
Here is a link to a nifty video explaining the sonic boom of an aircraft and all the other FUN facts that go along with it.
http://www.youtube.com/watch?v=-d9A2oq1N38&feature=related

Here is a link video showing a aircraft breaking the sound barrier, producing a sonic boom (you can even see the cone shape it makes!)
http://www.youtube.com/watch?v=QX04ySm4TTk&feature=relate


Ripple Tank Lab:

-The different colors in the lab represent the crests and troughs of a wave
-The ripples carry lots of energy, which is related to the amplitude of a wave, so...
-The dimmer the ripple becomes, the less energy it has; The brighter the ripple is, the more energy it has
Two Source Interference:
-When there are two sources sending out ripples, sometihng called interference fringes appear

Here's a pretty cool video showing two point source interference ripples. It's in 3-D and kind of gives a 360 view of the whole interference pattern. You can really see the crests and troughs well.

-Interference Fringes: "blackness"; nothing happens here; 'cancellation' of waves; ~ to nodes on a standing wave pattern
-When crests intercept troughs --> Interference Fringes occur (destructive interference); Nodal Lines
-When crests intercept crests or troughs intercept troughs --> constructive interference; Antinodal Lines

u12l3b1.gif
http://www.physicsclassroom.com/CLASS/light/U12l3b.cfm

In the diagram above, the red dots represent areas of maximum activity: where crests intercept crests and troughs intercept troughs. Connected together, they create the antinodal line. The blue dots represent areas of minimum activity: where crests intercept troughs. Connected together, they create the nodal line. In the real world, if you were sitting in a badly architected auditorium, the two sources (or more) of sound may overlap (as seen above). If this occurs, 'dead spots' occur, where you would have bad sound; if you sat here, you would not be able to hear much and probably have wasted your money (if you bought tickets). This means, when they construct large auditoriums (like Carnegie Hall or Bass Hall), they have to be careful of preventing interference fringes.


Here is a video clearly showing the interference pattern between two sources, causing the fringes to appear.
Can you spot the antinodal and nodal lines?

Path Difference - subtraction
PD = |S1 - S2|
*S1 and S2 = distance from Source one and Source two to Point A

u12l3b2.gif
http://www.physicsclassroom.com/CLASS/light/U12l3b.cfm

Ex) PDb = |3λ -4λ | = |-1λ | = 1λ
*Point B is on an antinodal line.
u12l3b4.gif
http://www.physicsclassroom.com/CLASS/light/U12l3b.cfm

Ex) PDd = |5-4.5λ | = |0.5λ | = 0.5λ
*Point D is part of a nodal line.
As shown above, points on an antinodal line have an integer path difference wavelength. Points on a nodal line have noninteger or fractional path difference wavelengths.
PD = m * λ
*m = order number
u12l3b6.gif
http://www.physicsclassroom.com/CLASS/light/U12l3b.cfm


Summary of the Path Difference Analysis
Point
antinode
or Node?

Order #
(m)

Distance
from S1 (in λ)

Distance
from S2 (in λ)

Path
Difference (in λ)

F
Node
2.5
2 λ
4.5 λ
2.5 λ
G
Antinode
2
4.5 λ
6.5 λ
2 λ
H
Node
1.5
2.5 λ
4 λ
1.5 λ
I
Antinode
1
3.5 λ
4.5 λ
1 λ
J
Node
0.5
2.5 λ
3 λ
0.5 λ
K
Antinode
0
6 λ
6 λ
0 λ
L
Node
0.5
5 λ
4.5 λ
0.5 λ
M
Antinode
1
3 λ
2 λ
1 λ
N
Node
1.5
6 λ
4.5 λ
1.5 λ
O
Antinode
2
6 λ
4 λ
2 λ
P
Node
2.5
4 λ
1.5 λ
2.5 λ
Young's Equation:
mλ=dSinθ
The order number multiplied by the wavelength is equal to the distance between the two sources multiplied by the Sin of the angle formed.
With two source interference, a Sin wave pattern is created. The crest of these waves match an order number created by the two source interference. The middle wave, which corrolates with the 0th order number, has the highest amplitude and is therefore the brightest.

The picture below is similar to the experiment we did in class to calculate the difference in grooves on old CDs. The difference is, Young did not use CDs to reflect, but sent the light beam through a slit. The front view of screen is similar to the pattern of light the laser made on the whiteboard in class.
u12l3c4.gif
http://www.physicsclassroom.com/Class/light/u12l3c.cfm


Below is an image of what happens when the light shines through the tiny slit: dark and light line pattern.
u12l3c1.gif
http://www.physicsclassroom.com/Class/light/u12l3c.cfm



This video, explained by Dr. Quantum (a true physics superhero!), demonstrates how water waves (or any other type of wave)
create an interference pattern when they pass through two slits.

LIGHT WAVES:
ELECTROMAGNETIC SPECTRUM
The Electromagnetic Spectrum relates radiation wavelengths and frequencies. It ranges from Radio and Micro waves to visible light all the way to X Rays and Gamma Rays. In a basic Electromagnetic Spectrum diagram, like the one below, both frequency and wavelength are mentioned and are important in discerning what type of wave/radiation it is. Like any other waves, the larger the wavelength, the lower the frequency and vice a versa. However, the electromagnetic spectrum really blends together, so there are many sections that overlap each other. But there are some generally agreed-on cutoff points for most of the sections of the spectrum.
Electromagnetic-Spectrum2.jpg
The electromagnetic spectrum shows you all the types of waves and their frequencies and wavelengths.


Here is a quick dissection of the Spectrum:
1. ELF -- Extra Low Frequency
- ranges from 1 Hz - 1 KHz
2. VLS -- Very Low Frequency
- ranges from 1 KHz - 300 KHz
- used in navigation systems, but information it can carry is limited.
- COOL FACT: BBC Coast and Shore Weather Centre sends out shipping forecasts at 198kHz (occassionally on VHF too)
3. AM Radio
- ranges from 300 KHz - 1.5 MHz
- AM: Amplitude Modulation
- bounce of ionosphere
4. Short Wave Radio
- 1.5 MHz - 30 MHz
- bounce of ionosphere
- used for CB radio (used mainly by truckers, police, and military)
5. VHF - Very High Frequency
- 30 MHz - 300 MHz
- a few meters in wavelength
- used for FM (Frequency Modulation) radio
- cool fact: the radio station number is the actual frequency of the wave
- used for Basic TV
6. UHF - Ultra High Frequency
- 300 MHz-3000 MHz (3000 MHz = 3 GHz)
- less than a meter in wavelength
- used for cellphones, bluetooth, wifi, cable TV and HDTV
- will soon be full because so many people use it.
7. Microwaves
-3 GHz - 300 GHz
- slightly overlaps UHF bands
- microwaves (that cook food) need water because that is what it jiggles to warm things up.
- interesting fact: contrary to Mom's beliefs, standing near a microwave will not give you cancer because a) the waves do not penetrate the skin and b) they wouldn't really come out of the microwave in the first place.
- centimeters in length
- used for radars
8. Infrared
- 300 GHz - 30 THz
- used for remote controls
- though you can not see it, your digital cameras can pick up the infrared radiation emitting from your controller when you push buttons.
9. Visible Light
- 1013- 1014 HZ
-lower limit -- wavelength=700 nm
- upper limit -- wavelength=400 nm
- out of the whole spectrum, this is the only section we can see
- Red, Green, and Blue are the primary colors of light
10. Ultraviolet
-1014 - 1017 Hz
- frequency in which visible light begins to be dangerous -- it can mess up molecules in your skin, causing skin cancer
11. X Rays, Gamma Rays
-10 17 - end of spectrum (approx.)
- X rays and Gamma rays are different not in frequency, but in how they are created
- X rays are ionizing waves and are formed when electrons are knocked off of atoms
- Gamma rays are formed with nuclear interactions (how light particles are formed)
- How do X rays (at the doctors office) work?
- your bones have metal in them (calcium and iron) that your tissues do not. X rays differentiate between those two and you can see your bones (and other foreign objects) on the screen.

FUN VIDEO:
Basically goes through the electromagnetic spectrum while giving examples of how each is used (ie radiowaves used for TVs, infrafred readiation for remotes, etc.). It also gives pictures of the examples. Downside: singer is slightly tone deaf.


FUN FACT: Did you know that Balck holes emit X-Rays?!
external image Black%20hole%20cartoon.jpg


Some more cool/gross stuff related to the Electromagnetic spectrum:
1. A cool website from NASA that goes into the spectrum with cool and interesting facts:
**http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html**

2. Ever wonder what a CB radio looks like?
PRO510XL.jpg
3. A short clip on how infrared works


4. Interesting X Ray Pictures
x-rays-01.jpg 05-13_NailGunAccident.jpgbizarro-halloweeny-x-ray.jpg
These people lived :)

Here's a link to a virtual tour through the Electromagnetic Spectrum for you to get a clearer understanding of the different types of waves:
http://www.pbs.org/wgbh/nova/gamma/spec_flash.html

Some Insight on Visible Light

Visible light is what we see with our eyes. Each color we see has a different wavelength within the visible spectrum.

spectrum.gif
The wavelengths for each color are displayed. For example, the wavelength of the color red is about 700 nanometers or 700 billionths of a meter. That's smaller than a germ!


How do we SEE? Well, we see things when they reflect light into our eyes. Here's how it works:
camera_eye.jpg
The way that our eye functions is similar to how a camera functions. Think of the retina as the film of a camera.
human_eye.jpg


1. The light reflected by objects is focused into our eyes by the cornea, which is the clear membrane that covers our iris (the colored part of our eyes). The cornea bends the light so that it feeds into our pupils, which are the holes in our irises.
2. The light is focused into the pupil, which contracts or enlarges to regulate the amount of light that enters our eyes. When we try to see in the dark, our pupils enlarge in order to let more light into our eyes, so we can see. When it's too bright, our pupils contract or get smaller to keep us from being blinded by too much light.
3. The light then enters the crystalline lens behind the pupil. The lens are transparent, and they focus the light to the back of our eye where the retina is. Keeping the lens in place are the ciliary muscles that can bend and manipulate the lens to help us see far-away objects and close-up objects. To see far-away objects, the ciliary muscles relax and stretch the lens, making it less convex and focusing the light more directly towards the retina. To see close-up objects, the ciliary muscles contract to make the lens more convex, which focuses the light coming from the nearby object towards the retina.
4. The light travels throught the vitreous humor, which is the jelly-like tissue that's between the crystalline lens and the retina.
5. The light reaches the retina. The retina is the tissue made of light-sensitive nerve cells in the back of the eye. These photoreceptor neurons change the light into an electric impulse and sends it to the brain through the optic nerve.
6. The electric impulse is sent to the brain, which then creates the image that you see according to the messsage it received from the optic nerve in the eye.

Why do things have color? Well, the reason is because every object absorbs light. For example, the sun emits all of the colors of visible light (you see the sun's light as white because all of the colors are mixed together, which creates white). When the sunlight hits an apple that you found lying on the ground, all of the colors of visible light EXCEPT FOR RED are absorbed by the apple. That means the colors violet, indigo, blue, green, yellow, and orange were absorbed by the apple, and the apple REFLECTED red! The apple reflected the red wavelength but not the other colors' wavelengths. Remember, WE ONLY SEE THE LIGHT THAT THINGS REFLECT. The colors that the apple absorbed are not reflected back to our eyes, so we do not see them. Only red color was reflected to our eyes. This is how we see things and their color.
seecolor.gif
White light contains all of the colors of visible light. Every color was absorbed by the apple except for red. The apple reflected the red light, and that is why you see the apple as red.
leaf.gif
Here's another picture on how we see color. This leaf absorbs every color of the visible light spectrum except for green, which it reflects.


As we've mentioned before, all of the colors of light mixed together create white. Remember that we also stated the primary colors of light are red, green, and blue. Why are the primary colors of light different from that of pigments (as in painting in art class)? To answer this question, remember how we see color. With paints, we only see the light reflected by the paint. Blue paint absorbs red and green light, but it actually absorbs more red light than green. (Note: We have previously used the term "all of the other colors of light." From the previous pictures on "seeing color," you see the sun emitting the rainbow. It is actually just emitting red, green, and blue, but these colors mixed to form the other colors like yellow. We are now going to use the primary colors instead of mentioning the other colors because in essence, objects do not absorb yellow light but rather red and green light combined to make yellow). If we were to mix the blue paint with yellow paint (which absorbs blue light), we would have a new paint that absorbs blue and red light, so that means the new paint reflects green. The way pigments (or paints) mix is different from the way light mixes, so that's why the primary colors are different for each.
paintmix.JPG
The circles of color represent the blobs of paint that we would mix. The letters above the circles indicate which colors each paint absorbs. For example, the blue paint absorbs red and green light. However, the G for green is significantly smaller than the R for red because there seems to be more red light being absorbed than green. When the paints combine, the new paint absorbs red and blue, so then it reflects green, making green paint.


The actual primary colors of pigments are magenta (red), cyan (blue), and yellow. Red and blue are just easier for younger children to remember (and spell!). When all three primary colors of pigments are mixed together, they make black. In the absence of pigment, there is white. This is the opposite with light. When the three primary colors of light are combined, they create white light. In the absence of light, there is black. The primary colors of pigments and the primary colors of light have a sort of inverse relationship; the primaries for one are the secondaries of the other.
primaries.gif
Here are the primary color of light and of pigment (or paint). They share an inverse relationship because the primary colors of light are the secondary colors of pigment, and the primary colors of pigment are the secondary colors of light. Notice the black and the white in the middle. They switch too!

For more about color and light and the mixing of lights, visit this website: Color and Vision- Color Subtraction
Here are some GREAT websites with REALLY COOL applets and interactive activities that'll help you explore the relationship between light and color:
http://micro.magnet.fsu.edu/primer/java/primarycolors/additiveprimaries/index.html
http://micro.magnet.fsu.edu/primer/java/primarycolors/subtractiveprimaries/index.html
http://www.learner.org/teacherslab/science/light/color/shadows/index.html
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/colorseparation/index.html
http://phet.colorado.edu/simulations/sims.php?sim=Color_Vision

So..how are rainbows made?
Rainbows are a result of the sun's white light being broken into the colors it is composed of through the prism of a raindrop.
This is called
. The light is often double-reflected on either side of the raindrop before exiting and headed your way. The color of a light wave see depends on the frequency of the light wave entering your eyes.

This explains why we see the colors of a rainbow. The colors line up next to eachother because different frequency light waves bounce and reflect differently, meaning that the different colors line up coming at a slightly different angle from each other. (remember that the frequency of a wave is the number of cycles of a wave to pass some point in one second.)


"Sharp Adds Yellow to 3-D TV"
http://gadgetwise.blogs.nytimes.com/2010/04/13/sharp-adds-yellow-to-3d-tv/?scp=1&sq=Colors%20of%20Light&st=cse
In the New York Times article, "Sharp Adds Yellow to 3-D TV," Sharp, as the title says, has added yellow to their spectrum of color for televisions. In the past, red, green, and blue have been the only colors used because they are the primary colors of light. R.G.B., as it is known to manufaturers, makes up all of the colors seen on the screen in various combinations. This addition of yellow changes the equations of the colors. With yellow, the colors are brighter because of a "higher light transmission through the panel and a wider gamut of colors." However, some worry that, because images have been filmed for R.G.B., they will look strange with the addition of yellow.

REFLECTION, DIFFRACTION, REFRACTION
When a wave hits a barrier, it will be reflected depending on the direction of the barrier. The angle between the incident wave and the normal (perpendicular; remember from the free body diagrams?) is the same as the angle between the normal and the reflected wave. See image: reflect.gif
When a wave travels through a small hole in a barrier, it bends around the edges. This is called diffraction. See image: diffrac.gif
When a wave enters a different medium (more shallow region) at an angle, the direction of waves changes. This change is called refraction. See image:
ShirleyDeng.gif


This is a video on the refraction and reflection of light.


The Eye:
external image NEA09.gif
Cornea: surrounds the eye and protects it from debris
Iris: the color part of the eye, surrounds the pupil
Lens: convex lens that inverses the image, which is then switched back in the brain; focuses light onto the retina; if deformed, need glasses
Retina: composed of sensory cells; reacts to light coming in; sends information to the brain
Optic Nerve: carries information to the brain
Retinal Tissue: two types, rods and cones
Rods: associated with detection of light intensity; helps detect difference in brightness; useful with night vision
Cones: associated with color vision; blue, green, and red sets of cones (also primary colors of light); green cones most sensitive set