[UPSC CSE 2011] Diffraction (Q262, 15M)

In relation to a plane diffraction grating having 5000 lines per cm and irradiated by light of wavelength 6000\,\mathring{\mathrm{A}}, answer the following:

(i) What is the highest order spectrum which may be observed?

(ii) If the width of opaque space is exactly twice that of the transparent space, which order of spectra will be absent?