CD Diffraction

Objective: CD's have very small grooves on them which make it possible to store music on them. Measure the distances between the groves on a CD by using a laser and diffraction.

Equipment:

• Laser
• Compact Disk
• Meter Stick
• A Screen with a hole in the middle.

Procedure: Arrange the  laser and screen so that the laser points through the hole in the screen and hits the CD with nearly normal incidence. (we used a white board to help mount the CD.

   Move the CD around as needed in order to see a diffraction pattern coming from the CD to the screen. Make it so that the first order maxima will appear on the screen on either side of the hole the  laser is coming through. (the zero order maxima strikes the hole so it is not seen. Once this happens the distance between the screen and the CD is measured, L, and the distance from the hole to the first order maxima is measured, x, (this part was done by marking on the screen the location of the maxima and measuring the length and dividing by 2). Also note the wavelength of the laser.
                      λ=633 nm              L=3.8 ± 0.02 cm          2x= 2.5 ± 0.1 cm

Using these calculations it is seen that our error is high from the standard manufacturer's standard value of 1600 nm. This error is accredited to the the fact that our experiment was not stable. We couldn't get the diffraction to show on our screen so for the experiment we held the CD (off the table) in order to get the diffraction to show on the screen. As a result our measurements were not very accurate because the CD was moving around slightly. But on the low side of our uncertainty we came up with a 9.31% deviation from the standard value.