1. The problem statement, all variables and given/known data A diffraction grating with 14100 lines per 2.54 cm (i.e., per in.) is used to view the visible spectrum from a Hydrogen gas excited by an electrical discharge. At what angle from the beam axis will the first order peak for the red photons with wavelength of 0.656 μm occur? 2. Relevant equations d sinΘ= m λ 3. The attempt at a solution I think i've got the right awnser, but apparent not. so here is what i've done , to get d : 0.0254m/14100 = 1.801E-6 Θ = sin^-1 ( 656E-9 / 1.801E-6 ) = 21.36ο . However, this is not the correct answer. I was wondering how I might have made a mistake?