How many lines per centimeter does a grating have if the third-order occurs at an 18.0 degree angle for 630 nm light?

The correct answer to this question is1635 lines per cm. This question would be found on a math test and could also be found on an IT test due to its difficulty. If one answers this correctly, along with many other questions on the test, the result is that they have a high IQ. The part of math that it corresponds to is diffraction grating.

This involves an optical component which as a periodic structure. The structure will split and diffract light into different beams, which will travel in different directions. It will also include a large number of parallel slits.

I will be honest, this is very out of my wheelhouse. However, after reading the last answer on this question: it’s still very out of my wheelhouse. So, I will attempt to answer. This is a diffraction question; that much is easy to explain. Diffraction is the act of spreading light around a room (like in a prysm).

This question seems to be asking how many lines of light are in a certain area of diffracted light.
I will be honest, I cannot answer this question. Once the math kicks in, you lose me. I would suggest you look online for an answer, since this is one of the few thing sI will not be able to answer, even with all the online searches in the world.