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An ideal fluid is a fluid that is incompressible and no internal resistance to flow (zero viscosity). In addition ideal fluid particles undergo no rotation about their center of mass (irrotational). An ideal fluid can flow in a circular pattern, but the individual fluid particles are irrotational. Real fluids exhibit all of these properties to some degree, ...


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A perfect, or ideal fluid is also incompressible, but an ideal gas is not. Pressure and volume changes on an ideal gas can cause changes in its density. A perfect fluid is described by an irrotational velocity vector field $\bf v$, so that $$\nabla \times \bf{v} =0$$ and this is not necessarily true for ideal gases. The molecules of an ideal gas interact ...


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The Fermi energy is the energy of the highest occupied/lowest unoccupied single particle state. For fixed volume, additional particles in the ground state go into the lowest unoccupied state increasing the Fermi energy, as you demonstrate. A temperature $T$ much less than the Fermi energy can only excite particles within roughly $k_B T$ of the Fermi surface. ...


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Because the heat energy remains the same and there is no expansion work done (expansion of gas while applying a force on a surface via pressure). This means that total energy is conserved. The energy of a molecule is its kinetic energy, 1/2mv^2, and the total energy is the sum of the kinetic energy of every molecule. To keep this sum from changing, the root ...


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The general answer is yes, the nature of the gas matter. The practical answer is; it depends. In your conditions, the effect might well be negligible.   As joseph established, if you are under the conditions where you can call your gas an ideal gas, the nature of it matters not. The P-V relation is simply given by, well, you guessed it, the ideal gas law.   ...


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Provided that the number of ideal$^1$ gas particles is the same, the pressure-volume relationship is the same for different ideal gases. Avogadro's law states that $$\frac{V}{n}=k$$ where $n$ is the number of mole and $k$ is a constant, meaning $$\frac{V_1}{n_1}=\frac{V_2}{n_2}$$ This tells us that even if the number of moles of a gas increases/decreases, ...


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Landau and Lifshitz, in their "Electrodynamics of Continuous Media", give the following expression for Rayleigh extinction coefficient $h$ (that's directly proportional to coefficient of scattering) in gases: $$h=\frac{2\omega^4}{3\pi c^4}\frac{(n-1)^2}N, \tag{120.4}$$ where $\omega$ is frequency of light, $n$ is refractive index of the gas, and $N$...


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You asked for a physically intuitive explanation, so here we go. For the full derivation, see Nanashi No Gombe's answer. I believe this "bump" phenomenon is related to the Skottky anomaly, which is explained nicely for a two state system in this wikipedia article: https://en.wikipedia.org/wiki/Schottky_anomaly. I will begin by explaining the "...


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