Design and perform a scientific experiment that illustrates how one the concepts works.

a. What is the “testable” question that the experiment is trying to answer?
How far apart are the data tracks?
Describe how you will test the question above. Provide a diagram or photograph of the experimental setup.
First you will need a used or new DVD or Cd which ever you would like to use and then you need a portable hand laser. Then you will point the laser at the dvd or cd and try to figure out how does a laser read the dvd or cd when it is being played.

Materials and Equipment
laser pointer (with known wavelength)
-CD
-DVD
-protractor
-index card
-several pieces of thin cardboard (cereal box, or similar)
-sturdy box, preferably wooden
-stack of books
-black marker
-calculator with trigonometry functions (sin, cos, tan)
-digital camera and tripod (optional)

1. Experimental Procedure
Laser Pointer Safety
Adult supervision recommended. Even low-power lasers can cause permanent eye damage. Please carefully review and follow the Laser Safety Guide.


1. The image above shows the experimental setup. It's a good idea to work near the edge of a table, with good lighting. Here are the important features of the setup, in order of construction:

a.Place the CD, label-side down, near the center of the workspace.

b. Put a piece of cardboard to the right of the CD, and another piece of cardboard behind the CD. Both pieces should be about the same thickness as the CD. You will be placing the box on top of all this. The cardboard prevents the box from wobbling.

c.If you want, put a piece of paper or tissue over the back half of the CD, to prevent scratching.

d. For measuring the angles, you will attach the protractor to the index card, flush at the bottom. Use a stack of two cardboard spacers at the points indicated, so that the laser pointer can shine down between the index card and the protractor.

e. Tape the index card to the side of the box (we used a wooden box for holding magazines). The index card and protractor should be flush with the bottom of the box.

f. Carefully place the box over the CD and cardboard pieces. You want the index card lined up along the diameter of the CD, parallel to the front of the table. The center of the protractor should be lined up midway between the center and the rim of the CD.

g. A stack of books makes a convenient elbow rest for the person holding the laser pointer. Rest your fingers against the box as shown to help hold the laser pointer steady.

h. Before you turn on the laser pointer, make sure that no one is in the path of the diffracted beams (the plane of the index card, extended out on both sides and above).

i. Direct the laser pointer beam down the face of the index card, and align the beam with the center of the protractor. You may have to fiddle slightly before you see a diffraction pattern like the one in the photo. Make your adjustments carefully, keeping the beam as close to parallel with the card as possible.

2. Making measurements

a. When the incident and diffracted beams are clearly visible, mark their locations with the marker, or take a digital photo for later analysis. If you are using a marker, start with a fresh index card for each measurement. If you are using a digital camera, make sure that the camera is aligned parallel to the index card, with the frame horizontally centered on the protractor. As a test, it's a good idea to take a picture of an index card marked with three lines at known angles. Measure the angles with your favorite photo editing program to confirm that your camera is aligned properly.


b. The image above shows how to mark and measure the angles. If you are using a marker, mark the beam locations with dots, and label them. If you are using digital photos, use a photo editing program to draw lines over the beams, starting from the center of the protractor. Remember that angles are measured from the normal (black line in the illustration). For example, θi, the angle of the incident beam, is 20 degrees in the image above. You measure from the normal (90° on the protractor) to the incident beam (70° on the protractor).[Note: Did you notice the small problem with this setup? Examine the protractor closely, and you will see that the positions for 0 and 180 degrees are not flush with the CD. Because of this, the angles measured with this setup will be slightly underestimated. A protractor that has 0 and 180 degrees flush with its edge is a better choice.]

c. Repeat the procedure at least five times. If you are using a marker, remember to start with a fresh index card for each measurement. It is OK to vary the angle of the incident beam with each trial

d. Do five trials with a DVD for comparison.

3. Calculating d, the data track spacing.

a. Make separate tables for your CD and DVD data, similar to the one below. You'll fill in the first five columns from your measurements, and you will calculate values for the last four columns. For some angles of the laser pointer, you may not see all of the diffraction orders. In that case, just leave the column corresponding to the missing order blank.

b. Here is the formula for calculating d:
d = m × λ ⁄ (sin θm − sin θi ) (Equation 2)

c. Calculate d for each of the non-zero order diffracted rays (i.e., m = +1, +2, −1, −2). For example, for m = −1, and a laser pointer with a wavelength of 655 nm, the formula would be:
d = (−1) × 655 ⁄ (sin θ−1 − sin θi )
Since we entered the wavelength in units of nm, our answer is also in nm. (To convert to μm, multiply your answer by 1 μm/1000 nm.)

d. Note: make sure that your calculator is set for entering angles in degrees.

e. If your laser pointer specifies its wavelength as a range of numbers, use the center of the range as the value for λ. Inexpensive red laser pointers are generally in the 635 – 670 nm range. Green laser pointers are 532 nm.

f. Calculate the average value for each d column, and, separately, for all of the values of d.

Source:
http://www.sciencebuddies.org/mentoring/project_ideas/Phys_p011.shtml?from=Home


b. Identify the VARIABLES (independent, dependent, and controls) being measured, with an explanation of how you will measure each of them.

Identify the Independent variable:
The independent Variable is the position of the laser on the cd.
How will the independent variable be measured?
This will be measured in Degrees on a protractor.

Dependent variable:
The dependent variable is the outcome of angles on the protractor reflected off the cd.
How will the dependent variable be measured?
This will be measured in degrees on a protractor.

Control(s):
CD, the distance on the CD the laser was pointing at 2 cm away from the bar code.
Why are these control(s) necessary?
These are very important because to get an accurate reading or your results will be wishy washy (even though i think my readind came out that way!!). Control means the things to keep consistant, and by keeping those things consistant is easier to read and retest the experiment.

c. Perform the experiment and organize your results (data) in a way that someone else could easily understand. Perform enough TRIALS to ensure you have reliable data. Use a table if necessary.

Test #1
Incoming Ray in Degrees	Outgoing Ray in Degrees
46	43
	18
	5
Test # 2
Incoming Ray in Degrees	Outgoing Ray in Degrees
30	30
	5
	60

d. Equation solving to see the data spacing between the data track.
d = m × λ ⁄ (sin θm − sin θi )
d= is the spacing of the structure (in this case, the data tracks).

θm= is the angle of the mth diffracted ray, and θi is the angle of the incident (incoming) light. Both angles (θm and θi) are measured from the normal, a line perpendicular to the diffracting surface at the point of incidence (where the light strikes the CD)

m= is the order of the diffracted ray. The reflected ray (when θm = θi) has order 0 (zero). Rays farther from the normal than the reflected beam have order 1, +2, +3, etc. Rays closer to the normal have order −1, −2, −3, etc. In certain cases, for example very small d, some or all of the negative m orders may actually be diffracted through such a large angle that they are on the same side of the normal as the incident light.

λ= is the wavelength of the light.

d = m × λ ⁄ (sin θm − sin θi )
Test # 1
(1)(532)/(sin18-sin46)= -28
(2)(532)/(sin43-sin46)= -354.6

Test #2
(1)(532)/(sin30-sin30)= 532
(2)(532)/(sin60-sin30)= 35.46

e. Your conclusions. Do your results lead you to infer an answer to your “testable” question? Why/why not? Explain thoroughly using your data to support your claims.
My experiment did lead me to a reasonable answer for each of my testes. But my answers are seem to be really fishy as in there are minus sighs in Test #1 which i dont think there should be any. I think something went wrong during the experiment to lead me to an unsure answer. this experiment leads me to question my own steps i took to get the data and the math it took to solve to get how far apart the data tracks are from each other?

f. A list of further questions you still have after performing the experiment.
-Is there another way or experiment to test the data tracks on the cd?
-Is the equation an accuret equation to slove for data tracks?
-Would there a different number for data tracks if u use a different color laser instead of a green or red laser?
-What other colors do lasers come in?
-Is the distance in between the data tracks the same?

g. How does your experiment connect to the gadget you took apart? Explain in atleast one paragraph.
My experiment does connect to my gadget because i got to see how the little laser in a DVD player reads the data tracks on a cd when it is playing. iIts pretty intersting to see and test out the angles a cd reflects off. For a cd to work in a DVD player the laser needs to read the data on the cd. My experiment got to test how strong the laser in a DVD player is how it works. The incoming ray will reflect off a different outgoing ray because it depends what postion you place the laser. That's why in a DVD play or CD player the laser is in a consistant postions only moving up and down which allows it to get the right measurement on the data track.

h. How would the results of your experiment be used by someone to desgin your gadget? Explain.
Knowing how far apart the data tracks are, lets you know how far the laser needs to move so it can read the next data track.




i. Provide links to other resources for further reading.
How does a laser work?- http://science.howstuffworks.com/laser2.htm

j. Include a bibliography that shows all your sources.