From the expression,
λ=c/v
we get,
v=c/λ
Where, ν = frequency of yellow light
c = velocity of light in vacuum = 3 × 108 m/*
λ = wavelength of yellow light = 580 nm = 580 × 10–9 m
Substituting the values in expression (i):
v=3108/58010-9=5.171014 -1
Thus, frequency of yellow light emitted from the sodium lamp = 5.17 × 1014 *–1
Wave number of yellow light v=1/λ
1/58010-9=1.72106 m-1