Diffraction grating — UPSC Physics Optional IFoS 2025 Paper I

A parallel beam of sodium light of wavelength 5893\text{ \AA} is incident on a diffraction grating. The angle between the first order spectra on either side of the normal is 27^{\circ} 42'. Find :

(i) The number of rulings/mm on the grating.

(ii) The greatest number of bright images obtained.