Problem 5.140

Light falls normally on a transparent diffraction grating of width \(l=6.5 \mathrm{~cm}\) with 200 lines per millimetre. The spectrum under investigation includes a spectral line with \(\lambda=670.8 \mathrm{nm}\) consisting of two components differing by \(\delta \lambda=0.015 \mathrm{nm}\). Find: (a) in what order of the spectrum these components will be resolved; (b) the least difference of wavelengths that can be resolved by this grating in a wavelength region \(\lambda \approx 670 \mathrm{nm}\).