Experiment 11: CD Diffraction

Purpose: Use laser diffraction to determine the distance between the grooves of a CD.

Materials:

Laser

CD

paper with small hole cut in it

meter stick

stands

clamps

Set Up:

First we needed to find the wavelength of the laser using a simple diffraction experiment. We measured the length (L) from the diffraction grating to the white board. Then we measured the distance (y) from the middle red dot to an adjacent red dot. And the distance between slits on the diffraction grating (d) was given to be 500lines/mm.

Data:

Now we need to caluclate the d between the grooves of a CD by shining the laser on it and using the same equation and wavelength just calculated. By cutting a hole through a piece of paper, we shined the laser through it and the relfection from the laser bounced back and left dots on the backside of the paper. Now we could find y again.

Calculations:

Conclusion:

Our experiment had a 20% error since our measured distance (d) was 1280 nm and the actual distance was 1600 nm. This is a pretty decent result using this procedure, although most of the other groups got a value close to 1600 nm.