Problem: The two most prominent wavelengths in the light emitted by a hydrogen discharge lamp are 656 nm (red) and 486 nm (blue). Light from a hydrogen lamp illuminates a diffraction grating with 540lines/mm, and the light is observed on a screen 1.3mbehind the grating.
Part I: What is the distance between the first-order red and blue fringes?
Can someone please explain what the heck is going on?