Experiment 12:CD Diffraction

Introduction:

In this experiment, the distance between the grooves on the DCDs had to be measured by using the laser and the concept of diffraction.

The equipments used for this experiment were the laser, Compact Disk, large screen (wooden blocks in our experiment), meter stick.

The really conducting of this experiment was using the laser and pointing it to the shinning side of the CD or DVD, the laser would then be reflecated to a certain distance on the screen. In our experiment, DVD was used and the standard distance between the grooves is 760 (nm).When the experiment was doing, the reflected center point had to be reflected back to where the laser pointer sent out the laser. Then both of the reflected dots, the first order maxima would be found on the screen. Conceptually, the distance between each dot and the central point had to be the same. Therefore, the distance x, which is the distance between one of the first order maxima dot and the central dot, would then be measured. Without the screen being moved, measured the distance between the DCD and the screen. Since the laser pointer being used is the Helium-neon laser, the wavelength of 632.8 (nm) then would be applied.

The distance for grooves needed to be obtaind

 the setup of this experiment

 the laser is reflected to the screen(the wood)

both dots on the wood represented the first order mixima

Given Data:

λ=632.8x10^-9

standard value for the grooves' distance: 760 (nm)

Measured Data:

L=11.7 +/- 1 (cm)

x=19.65 +/- 1(cm)

Calculation:

Calculate θ first: tan(θ)=10.65/22.7

                             θ=tan^-(19.65/11.7)=59.23

                             sin(θ)=λ/a 

                             a= λ/sin(θ)=632.8x10^-9/sin(59.63)=736(nm) 

Percent Error:

|(736-760)/760|x100%= 3.158%

 

Conclusion:

When the experiment was conducting, the relationshoip between the distance between the CD and the screen, and the distance between the first order maxima and the central point is proportional to each other. In other words,. no matter how far the screen was moved, the angel for the first order maxima would not be changed. When the screen was moved further, the distance between the central dot and the first order dot would also increase, hence the angle between stayed constant. In this experiment, the percent error calculated was  3.158% , which was within 10% error, the error could be contributed by the efficiency of the laser pointer, and also the accuracy of the distance's measurements. Based on the diffraction concept, the area between these two first ordr maxima dots was the dark area, as well as where the wave destructed, if one much larger screen was used, then the second order maxima, or even the third order maxima could also be obtained, too.