Question

A parallel beam of sodium light is allowed to be incident normally on a plane grating
4250 lines per cm and a second order spectral line is observed to be deviated through
30º. Determine the wavelength of spectral line.​

Answer 1

Given :

N = 4250 lines/cm

θ = 30°

To find :

Wavelength of spectral lines

Solution :

d sinθ = n λ

d = 1 / N

d = 1 / 4250 cm

d = (1 / 4250) × 10⁻² m

(1 / 4250) × 10⁻² × sin30° = 2 × λ

λ = 5.882 × 10⁻⁷ m

λ = 5882 × 10⁻¹⁰ m

λ = 5882 Α

The wavelength of spectral line is 5882 A