Diffraction Practice Problems
A sodium vapor lamp emits two yellow-orange color wavelengths (λ 1 = 589.0 nm and λ 2 = 589.6 nm). When these two wavelengths pass simultaneously through a diffraction grating, a diffraction pattern corresponding to the first-order diffraction (m = 1) is observed on the screen (figure below). The spectroscopist considers that the two peaks are resolved if the difference between y 2 and y 1 is at least equal to the peak's full width at half maximum (FWHM). Note that for small angles, the first order of diffraction of a diffraction grating and the m = 1 interference fringe of a double slit share the same spatial position. Determine y 2 - y 1 in terms of λ 2 - λ 1, L (the distance between the double slits and the screen), and d (the separation between the two slits).