# Diffraction Gratings

1. Apr 19, 2013

### MarcL

1. The problem statement, all variables and given/known data

A grating places a spectral line of wavelength 681 nm at 12 degrees in first order. At what angle is a line of wavelength 439 nm observed in second order?

2. Relevant equations

I believe dsinθ= mλ

3. The attempt at a solution

This is where I get lost, I can solve for every problem in difraction ( We did Rayleigh's criterion, double slit / single slit difraction) but I can't seem to be able to start a problem that involves grating, any pointers on how to start would be nice ^^ I just want to know how to approach the problem! :)

2. Apr 19, 2013

### TSny

As far as finding the angles for the bright fringes, there is no difference between a grating and a double slit.

One approach to this problem would be to use the information about the 681 nm line to determine the distance d between two slits in the grating.

3. Apr 19, 2013

### MarcL

Ah, it worked. Thanks a lot ^^ Just a little question, if you don't mind answering it of course. If ever it asked me to look for the distance between the two waves, would I need to compare the equations or something?

4. Apr 19, 2013

### TSny

Good!

I'm not sure what you mean by "distance between the two waves". Can you clarify that?