Science Buddies: "Ask an Expert"

Hello!

For the experiment: "Measure Data Track Spacing on a CD using a Laser", my science teacher and I performed the experiment, and we calculated all the data, we just have no idea what the results of the equations mean. If someone could tell us what they are, that would be amazing!

Thank you!!

i<3ciencias,

The experiment is here, correct? https://www.sciencebuddies.org/mentorin ... p011.shtml

Could you post your data? That would help us to help you.

Adam

so using the equation, these are the results:

m=1: 1544nm
m=-1: 1915nm
m=-2: 1614nm

now we weren't sure how to do m=0, because multiplying an equation by zero would just make the answer zero, so what's the point of even having it? that was also confusing.

so now that we have these measurments, what do they mean?

Thank you!!

yes, that is the project link.

Heather,

Your data seems to suggest that the spacing between tracks is about 1550 nm. However, your data for m=-1 seems a bit off--did you run the experiment several times? Is 1915 nm the average for m = -1?

Adam

Also, don't calculate the m = 0 case.

m is used to represent the number of diffraction angles away from the 0th order reflection, so what you'd end up with is 0/0.

yeah, it could have been off. that wasn't acctually the real experiment. my teacher and i were just going through likea dry run to make sure we could acctually do this successfully.

how did you get 1550 nm? do you do an average or something?

that's where we are confused.

thank you!

Heather,

Yes, I just averaged the two--after you go through the experiment several times, you might get more precision with your measurements which will get you closer to the actual value for d. A quick search of the net reveals a value of 1.6 microns (which is the same as 1600 nm, or .0016 mm),--so you're certainly on the right track.

If you have any more questions, either before or after you perform the complete experiment, feel free to come back and post them!

Have fun and good luck!

Adam

I'll add quickly that under ideal conditions, all your values for d should be the same for a given medium (CD or DVD) as the grating spacing is uniform.

In experiment, you'll get some deviation, and it's a good habit to think about what the sources for the deviation or error might have been.

Thank you Adam!

You have been soooo much help to my science project and I!!!

- Heather

Hi there,

Another student asked a question last week about the formulas and what they meant. I and some other people helped him by directing him to a couple of sites with many explanations.

Check: https://www.sciencebuddies.org/mentorin ... php?t=1856

Good luck !