Diffraction Lab

Purpose:

The purpose of this lab was to test the diffraction of light against a compact disc.  A compact disc contains information by having small burns on the disk, these burns can be viewed by shining a lazar light onto the CD.  The equation used was:

y=mLR/2d

where y is distance from central maxima, m is number of minima, L is wavelength, R is distance from diffraction gradient, and d is distance between gratings which is our target variable in this experiment.

Method:

The experiment was assembled by using a standard compact disc and a laser with a wavelength of 670 nm +/- 20 nm.  Two sets of data were taken.  The first was at a distance of 2.00 m +/- .15 m.  At this distance the maxima were measured on the right of the central maxima and on the left of the central maxima.  To our surprise the two sides were different and one of the sides was also noted to be curved.  both sides were measured and charted.

	right (cm)	left (cm)	average (cm)	Uncertanty (cm)
m1	2.12	3.10	2.61	0.98
m2	4.70	5.50	5.10	0.80
m3	6.80	8.60	7.70	1.80
m4	8.60	11.10	9.85	2.50
m5	10.40	14.40	12.40	4.00

The varying values leads to a high uncertainty and makes the data less useful than desired.  Next we set up the experiment in a different way.  We place a white board close to the CD and place the Laser close to the CD as well.  By lowering the distance from grating to diffraction pattern we reduced the uncertainty of the data.  With a new R= 0.07 m +/- 0.015 m we got consistent data on both sides of the central maxima

	average (cm)	Uncertanty (cm)
m1	2.80	0.20
m2	4.20	0.40

Using our equation for diffraction grating we determined a value of d= 977.1 nm +/- 279.5 nm

Conclusion:

The value obtained for the distance between gratings was 977.1 nm +/- 279.5 nm.  The actual known value of the distance is around 1600 nm which is out of our uncertainty range and has an error percent of  21.5% from the furthest reaches of our uncertainty.  Although the data is on the same order of magnitude when uncertainty is taken into account, the actual results are not accurate at all.  Results may have been off due to having R be to small, if slightly larger measurements of minima distances would have been easier to get.