This question is about using a diffraction grating to view the emission spectrum of sodium.
Light from a sodium discharge tube is incident normally upon a diffraction grating having 8.00 x 10^5 lines per meter. The spectrum contains a double yellow line of wavelengths 589 nm and 590 nm.
Determine the angular separation of the two lines when viewed in the second order spectrum.
For this question, I first used the resolvance equation R=average wavelength/difference in wavelength= m x N (mth order of diffraction, N number of slits or lines)
The answer is 0.2 degrees, please can anyone smart enough answer this extremely difficult question? This is from a high school physics textbook.