Using a Laser Pointer to Measure the Data Track Spacing on CD

[ANB]

I have a couple of questions. Do the CD and DVD need to have data on them to find the spacing with the laser? When you calculate each angle of the diffracted beams, do you find the angle by measuring from the perpendicular line to the diffracted beam?

[MelissaB]

Hi,

I have split your post off from the old topic so that experts can see that there is a new question. Good luck!

[deleted-71588]

Study the labels on the picture under "2. Making measurements" https://www.sciencebuddies.org/mentorin ... p011.shtml to see how the angles are defined to match the equations.

I suspect that this project was originally intended to be done on mass produced CD and DVD pressings. I'm not sure what happens if you try it on a CD-R (designed to be written once) or a CD-RW (designed to be erased and rewritten) or a writable DVD.

I recommend that you first try your setup out on a pressed version. Once you know how to obtain the measurements, then try it on the other media types and see what happens.

[ANB]

Thank you. I have another question though. In the picture there is no m=+2. Will this angle come in between m=0 and m=+1 or will it come in front of +1 like -2 comes in front of -1? Are there supposed to be 6 or 5 angles of diffraction?
I really need a reply ASAP

[ANB]

Ok I think I read another reply and figured it out. There are supposed to be 6 angles of diffraction right?

[deleted-71588]

There are no set number of angles of refraction that you will get. The incident angle that you choose can affect the result as well as other factors. That is part of what makes this an experiment that has no known apriori answer. If you get at least three refracted beams from a given incident angle, you have enough to do the calculations. If you get more refracted beams, then you can improve your calculations to make a more precise determination of the track spacing with less error tolerance.

In any case, the number of refracted beams that you see is what you see/get to work with.