ABSTRACT
We have shown in Section 3.1 of the textbook that the number of modes in the unit volume and the unit of frequency is () N = N v = 1 V d N ( k ) d ν = 8 π v 2 c 3 . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429092053/5e12ab0e-ba42-4caa-9bdf-6325e9117d3e/content/eqn3_1.tif"/>
