# Homework Help: diffraction grating ques

1. Dec 13, 2008

### noobie!

1. The problem statement, all variables and given/known data
Monochromatic light from a helium-neon laser(lambda=632.8nm) is incident normally on a diffraction grating containing 6000lines/cm.Find angles at which the 1storder,2nd..

2. Relevant equations

3. The attempt at a solution
here goes my solutions,
given lambda=632.8 X 10^9 ,but 6000lines/cm what does it mean?is that represents d,distance?i have no idea how to start,can you please hint me,thanks...

2. Dec 13, 2008

### heth

Re: diffraction grating ques..

Imagine a little fence which is constructed with four fence posts per meter. What is the spacing between the posts?

3. Dec 13, 2008

### noobie!

Re: diffraction grating ques..

hmm..umm is that mean its actually refers to coverage of an area?so 6000lines/cm X10^-2 change into 6000lines/m and then use d formula d=l/N ???but i can't get the answer..

4. Dec 13, 2008

### heth

Re: diffraction grating ques..

The units for your grating are "lines per cm". Just like the units for the fence are "posts per m".

No mention of area at all in the problem.

If you work out how to calculate the distance between the posts (which is easier to imagine than lines you can't really see) then you can use the same method to calculate the distance between the lines.

If you can't see how to use that, I'd suggest going back to your textbook and writing out in words what each of the letters in the equation you're trying to apply represents, and thinking about what the values would be for your problem.

5. Dec 13, 2008

### noobie!

Re: diffraction grating ques..

ok,i got you,i use d=l/N ; l= 10^-2 , N =6000 thus, 10^-2/6000 so my d =1.67 X 10^-6 afterall i shall applied sin@=m X lambda / d .........CORRECT???