Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wave number 
of the yellow light.
Given:
Wavelength of Yellow Light = 580 nm.
To Find Frequency of the light:
We know the following basic relation,
Speed of Light = [Frequency] × [Wavelength]
We know speed of light = 3×108 m/s
Frequency, v = [3×108] / [580 × 10-9]
v = 5.17×1014 Hz
Wave Number is defined as the number of wavelengths which can be accommodated in one centimetre of length in the direction of propagation.
Wave Number for Yellow Light = [1] / [λ]
= [1] / [580 × 10-9]
= 1.7 × 106 m-1
Therefore, the frequency of yellow light is 5.17×1014 Hz and the wave number of yellow light is 1.7 × 106 m-1
8