Experiment 12: CD&DVD DIFFRACTION

10/11/2012

The purpose of the experiment is that the grooves on the CD and DVD. And compare to the manufacturer's standard value.

Equipment for the experiment: Laser, CD & DVD, a paper with a small central hole, meter stick.

First, we placed the paper with a hole by two wood. Make sure the laser go through the hole and then place the CD and DVD on the other side. Try your best to make the CD and DVD perpendicular to the laser and measure the distance between CD, DVD and the paper. 

Try to make the all dots show on the paper.

The first one is for CD and the second one is for DVD. Because the distance between the grooves are different and we want to make it easy to measure the two bright dot we place DVD much closer to paper. Then we use pen mark it down. And use rule to measure the distance.

Then, we use the equation from the class which showing below.

The CD grooves distance we got is 1590nm which is closed to 1600nm. And the DVD we got is 743nm. And to explain the equation, because this is the first order maxima, so m=1. Then d=a.We follow the equation sin(theta)=lumda/d theta is angle which the dot is bright. but d=a so we can use this equation to find a. And this is exactly a triangle. So use the geometry to solve for a which we got is 1590nm for CD and 743nm for DVD. So this experiment we got almost correct measurement. And we learn how difference the distance between CD and DVD, because DVD can storage more information, so the distance should be closer so that can storage more. And base on the technology,that's why CD is cheaper than DVD.