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# Using A Laser To Track Spacing On DVD's And CD's

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by

## kiara blue

on 3 December 2014

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#### Transcript of Using A Laser To Track Spacing On DVD's And CD's

results

USING A LASER TO TRACK SPACING ON DVDS AND CDS
problem/question
procedures

hypothesis

My hypothesis is that,the wavelength of the laser is within the range of the wavelength of its color, which is 630mm to 650mm. In addition to this the width of tracks for a CD is approximately 1.6 μm and for the DVD it is 0.74 μm. The difference in widths of tracks is due to the fact that both the CD and DVD have different storage capabilities therefore the spacings are different.
materials

conclusion
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.

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)

You've probably noticed the colorful patterns "reflecting" from the shiny surface of a CD disk. What you are seeing is actually diffraction of white light, and the rainbows of color are diffraction patterns. In this project you'll learn about how diffraction patterns are generated, and you'll find out how you can use a laser pointer and a protractor to measure the microscopic spacing of data tracks on a CD.

What is a CD's data track spacing?

Problem
When different genres of music are put into the computer some take longer to recognize than others, I'm wondering if the data track spacing has anything to do with that.

Is the data track spacing on CD's different?

Specific Question
Do different genres of music have different data track spacing?
The average data track spacing on the DVDs was half the number of the
average data track spacing on the CDs, thereby showing the hypothesis
was backed by the data. The experiment will prove tha the data track
spacing of a CD is greater than the data track spacing of a DVD. If
using a green and red laser pointer to measure the data track spacing
on CDs and DVDs, then the data will prove that DVDs have smaller
spacing than CDs, because DVDS withhold a greater amount of information
than CDs. In future testing, it would be recommended to realize how
extremely difficult this project is and be able to take it head on, so
it can b done neatly and carefully. Other follow up experiments could
see if drawing with a sharpie over the CD/DVD will affect how the laser reads it
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