A diffraction grating is made up of slits of width 420 nm with separation 1300 nm. The grating is illuminated by monochromatic plane waves of wavelength ? = 790 nm at normal incidence.
(a) How many maxima are there in the full diffraction pattern?
(b) What is the angular width of a spectral line observed in the first order if the grating has 1000 slits?