The universe is filled with photons left over from the big bang that today have an average energy of about 2 × 10−4 ev (corresponding to a temperature of 2.7 k). as derived in lecture, the number of available energy states per unit volume for photons is

The number of available energy states per unit volume is

Explanation:

Given that,

Average energy  

Photon =

We need to calculate the number of available energy states per unit volume

Using formula of energy

Where, E = energy

h = Planck constant

c = speed of light

Put the value into the formula

Hence, The number of available energy states per unit volume is

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frequency or wavelenth of em radiation in a vacuum