# Thermodynamics and Statistical Physics [GATE (Graduate Aptitude Test in Engineering) Physics]: Questions 82 - 82 of 82

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## Question 82

Appeared in Year: *2017*

### Describe in Detail

Essay▾The energy density and pressure of a photon gas are given by and , where is the temperature and is the radiation constant. The entropy per unit volume is given by . The value of is ________. (up to two decimal places) .

### Explanation

The energy density of a photon gas is given as,

Since, ;

Now, Heat capacity is given by,

Now, entropy of photon gas is,

Entropy per unit volume,

According to question,

Substituting value of , from equation (1) ,