Question

Monochromatic light beam a helium-neon laser (λ = 632.8 nm) is incident normally on a diffraction grating containing 6000 grooves per centimeter. Find the angles at which the 1^st and 2^nd order maxima are observed. What if we look for the 3^rd order maxima? Do we find it?

Answer 1

First we must calculate the slit separation, which is equal to the inverse of the number of grooves per centimeter.

because sinθ cannot exceed unity, this does not represent a realistic solution. Hence only zeroth 1^st & 2^nd order maxima are observed for this situation