[UPSC CSE 2008] Diffraction (Q270, 20M)

Calculate the Fraunhofer diffraction pattern from a grating of N slits with width e, separated by equal opaque spaces d. Find the condition for principal maxima and the corresponding values of intensity. A parallel beam of Na light is incident normally on a plane grating with 4250 lines per cm. The second order spectral line is observed to be deviated through 30^\circ. Calculate the wavelength of light.