Diffraction grating used in the lab ?

Question

How do i know which side of the grating is ruled ?

Answer 1

Once you touch a diffraction grating the next thing you do it throw it in the garbage because it will be ruined. I assume this is not a transmission grating or it wouldnt matter. The easiest way is to just use it as a mirror to look at white light, if you see a rainbow that is the side that is ruled. If you are asking which way the ruling is blazed I think you have to just look for an arrow on it, unless you want to make a measurement from each direction and see which one has the larger amount reflected into the 1st order. (disregard last sentence if you arent worried about blazing)

Answer 2

Ask your teacher, different gratings have different ways of marking which side is ruled.

If the teacher won't answer, just touch it and you can feel the difference.  Of course having your fingerprints on optical equipment isn't good, but if the teacher won't tell you, then it's his fault.