photon gas

As a result, the chemical potential of the black body photon gas is zero.

The most common example of a photon gas in equilibrium is black body radiation.

The following table summarizes the thermodynamic state functions for a black body photon gas.

This means that the space inside the cylinder will contain a blackbody-distributed photon gas.

It is seen that the enthalpy is the amount of energy needed to create the photon gas.

The thermodynamics of a black body photon gas may be derived using quantum mechanical arguments.

This process can be continued at a constant temperature until the photon gas is at a volume V .

The spectral radiance, pressure and energy density of a photon gas at equilibrium are entirely determined by the temperature.

As an example of a thermodynamic process involving a photon gas, consider a cylinder with a movable piston.

Integrating over frequency and multiplying by the volume (V ) gives the internal energy of a black body photon gas:

Prevost considered that what is nowadays called the photon gas or electromagnetic radiation was a fluid that he called "free heat".

As photon gas expanded and cooled, some fermions would be left over (in extremely small amounts 10) because low energy photons could no longer break them apart.

A photon may collide with an electron in the wall, exciting it to a higher energy state, removing a photon from the photon gas.

This electron may drop back to its lower level in a series of steps, each one of which releases an individual photon back into the photon gas.

Blackbody radiation among various types of photon emission employs the photon gas model with thermalized energy distribution without interphoton interaction.

In a blackbody enclosure that contains electromagnetic radiation with a certain amount of energy at thermodynamic equilibrium, this "photon gas" will have a Planck distribution of energies.

The behavior of thermal phonons is similar to the photon gas produced by an electromagnetic cavity, wherein photons may be emitted or absorbed by the cavity walls.

A very important difference between a gas of massive particles and a photon gas with a black body distribution is that the number of photons in the system is not conserved.

For a photon gas in thermodynamic equilibrium, the internal energy density is entirely determined by the temperature; moreover, the pressure is entirely determined by the internal energy density.

In a similar manner, even photons (light quanta), if trapped in a container space (as a photon gas or thermal radiation), would contribute a mass associated with their energy to the container.

In physics, a photon gas is a gas-like collection of photons, which has many of the same properties of a conventional gas like hydrogen or neon - including pressure, temperature, and entropy.

In a photon gas, there will also be an equilibrium distribution, but photons do not collide with each other (except under very extreme conditions) so that the equilibrium distribution must be established by other means.

An ideal gas of bosons (e.g. a photon gas) will be governed by Bose-Einstein statistics and the distribution of energy will be in the form of a Bose-Einstein distribution.

If the photon gas is not initially Planckian, the second law of thermodynamics guarantees that interactions (between the photons themselves or photons and other particles) will cause the photon energy distribution to change and approach the Planck distribution.

If the photons are absorbed and emitted by the walls of the system containing the photon gas, and the walls are at a particular temperature, then the equilibrium distribution for the photons will be a black body distribution at that temperature.