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Adiabatic Processes for an Ideal Gas01:18

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When an ideal gas is compressed adiabatically, that is, without adding heat, work is done on it, and its temperature increases. In an adiabatic expansion, the gas does work, and its temperature drops. Adiabatic compressions actually occur in the cylinders of a car, where the compressions of the gas-air mixture take place so quickly that there is no time for the mixture to exchange heat with its environment. Nevertheless, because work is done on the mixture during the compression, its...
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Experimentally, if object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is in equilibrium with object C. That statement of transitivity is called the "zeroth law of thermodynamics." For example, a cold metal block and a hot metal block are both placed on a metal plate at room temperature. Eventually, the cold block and the plate will be in thermal equilibrium. In addition, the hot block and the plate will be in thermal equilibrium.
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Systems in mechanical equilibrium exert equal pressure on the separating wall. Similarly, systems in thermal equilibrium share a common thermodynamic property: temperature.Temperature is a measure of the average kinetic energy of particles within a system. More generally, it reflects the internal energy state of the system. The higher the temperature, the more energy a system has, given that other variables, such as volume and pressure, remain constant. However, temperature is not a form of...
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The definition of temperature in terms of molecular motion suggests that there should be a lowest possible temperature, where the average kinetic energy of molecules is zero (or the minimum allowed by quantum mechanics). Experiments confirm the existence of such a temperature, called absolute zero. An absolute temperature scale is one whose zero point is absolute zero. Such scales are convenient in science because several physical quantities, such as the volume of an ideal gas, are directly...
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Consider an adiabatic system composed of two chambers, A and B, designed such that no heat flows into or out of the system. Initially, chamber A is filled with a gas at a fixed temperature T1, pressure p1, and volume V1, while chamber B is evacuated. The gas is then gradually forced through a rigid, porous barrier to chamber B, ultimately reaching temperature T2, pressure p2, and volume V2. A piston on the right side maintains a constant pressure (p2), which is lower than p1. The significant...
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The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
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Characterization of Thermal Transport in One-dimensional Solid Materials
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Physics of negative absolute temperatures.

Eitan Abraham1, Oliver Penrose2

  • 1Institute of Biological Chemistry, Biophysics, and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.

Physical Review. E
|February 18, 2017
PubMed
Summary
This summary is machine-generated.

Negative absolute temperatures are thermodynamically valid and were experimentally achieved in nuclear spin systems. Counterarguments based on classical entropy formulas are flawed and inconsistent with experimental data.

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Area of Science:

  • Thermodynamics
  • Statistical Mechanics
  • Quantum Physics

Background:

  • Negative absolute temperatures, introduced by Purcell and Pound for nuclear spins, remain controversial.
  • A recent claim suggested negative temperatures violate statistical thermodynamics principles based on Gibbs' classical "volume" entropy formula.

Purpose of the Study:

  • To provide a thermodynamic analysis confirming the validity of negative absolute temperatures in experiments.
  • To examine and refute arguments against the negative temperature concept.
  • To demonstrate the inconsistency of the "volume" entropy formula with experimental results.

Main Methods:

  • Thermodynamic analysis of negative temperature systems.
  • Examination of arguments against negative absolute temperatures.
  • Comparison of theoretical predictions with experimental data on nuclear spins.

Main Results:

  • The thermodynamic analysis supports the negative-temperature interpretation of Purcell-Pound experiments.
  • Arguments against negative absolute temperatures are found to be logically uncompelling.
  • The classical "volume" entropy formula yields predictions inconsistent with experimental nuclear spin results.

Conclusions:

  • Negative absolute temperatures are theoretically sound and experimentally validated.
  • The "volume" entropy concept is inconsistent with observed phenomena.
  • The Purcell-Pound experiments successfully demonstrated negative absolute temperatures.