# Quick Optics Question on Gratings (Small calculation)

1. Jan 21, 2008

### _Mayday_

Hey,

Well, just a quick question, if a grating had 3,000 slits per mm, what would the distance between groves be? Is it 1mm/3,000 which would give me the grove distance?

2. Jan 21, 2008

### _Mayday_

So 1/3000 = 3.33x10^-4 is the distance between gooves?

3. Jan 21, 2008

### Staff: Mentor

Sounds right to me.

In mm.

4. Jan 21, 2008

### _Mayday_

^ When using using the formula $$n \lambda = d \sin(\theta)$$ trying to find the wavelength would I use it in mm?

I've basically conducted an experiment, using a sodium lamp and spectrometer, and want to see how accurate it is by comparing my results with an online result, but am having trouble finding a source that tells me the wavelengths, that I can compare to with my results.

5. Jan 21, 2008

### Staff: Mentor

When using that formula, the wavelength will have whatever units "d" has. You can always convert it to more convenient units, such as nm.

This might help: http://hyperphysics.phy-astr.gsu.edu/Hbase/quantum/sodium.html#c2"

Last edited by a moderator: Apr 23, 2017
6. Jan 21, 2008

### _Mayday_

I swear I saw a blue line aswell though? For the orange line i got 5.7x10^-5 mm, i dont know hwo accurate that is.