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<img src='https://ui.adsabs.harvard.edu/styles/img/transparent_logo.svg' alt='The CODATA 2017 values of h, e, k, and N A for the revision of the SI”>The CODATA 2017 values of h, e, k, and N A for the revision of the SI: Sufficient progress towards redefining the International System of Units (SI) in terms of exact values of fundamental constants has been achieved. Exact values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant N A from the CODATA 2017 Special Adjustment of the Fundamental Constants are presented here. These values are recommended to the 26th General Conference on Weights and Measures to form the foundation of the revised SI.
Re-estimation of argon isotope ratios leading to a revised estimate of the Boltzmann constant: In 2013, NPL, SUERC and Cranfield University published an estimate for the Boltzmann constant (de Podesta et al 2013 Metrologia 50 354-76) based on a measurement of the limiting low-pressure speed of sound in argon gas. Subsequently, an extensive investigation by Yang et al (2015 Metrologia 52 S394-409) revealed that there was likely to have been an error in the estimate of the molar mass of the argon used in the experiment. Responding to Yang et al (2015 Metrologia 52 S394-409), de Podesta et al revised their estimate of the molar mass (de Podesta et al 2015 Metrologia 52 S353-63). The shift in the estimated molar mass, and of the estimate of k B, was large: -2.7 parts in 106, nearly four times the original uncertainty estimate. The work described here was undertaken to understand the cause of this shift and our conclusion is that the original samples were probably contaminated with argon from atmospheric air.
In this work we have repeated the measurement reported in de Podesta et al (2013 Metrologia 50 354-76) on the same gas sample that was examined in Yang et al (2015 Metrologia 52 S394-409) and de Podesta et al (2015 Metrologia 52 S353-63). However in this work we have used a different technique for sampling the gas that has allowed us to eliminate the possibility of contamination of the argon samples. We have repeated the sampling procedure three times, and examined samples on two mass spectrometers. This procedure confirms the isotopic ratio estimates of Yang et al (2015 Metrologia 52 S394-409) but with lower uncertainty, particularly in the relative abundance ratio R 38:36. Our new estimate of the molar mass of the argon used in Isotherm 5 in de Podesta et al (2013 Metrologia 50 354-76) is 39.947 727(15) g mol-1 which differs by +0.50 parts in 106 from the estimate 39.947 707(28) g mol-1 made in de Podesta et al (2015 Metrologia 52 S353-63). This new estimate of the molar mass leads to a revised estimate of the Boltzmann constant of k B = 1.380 648 60 (97) × 10-23 J K-1 which differs from the 2014 CODATA value by +0.05 parts in 106.
New measurement of the Boltzmann constant k by acoustic thermometry of helium-4 gas: The SI unit of temperature will soon be redefined in terms of a fixed value of the Boltzmann constant k derived from an ensemble of measurements worldwide. We report on a new determination of k using acoustic thermometry of helium-4 gas in a 3 l volume quasi-spherical resonator. The method is based on the accurate determination of acoustic and microwave resonances to measure the speed of sound at different pressures. We find for the universal gas constant R = 8.314 4614(50) J·mol-1·K-1. Using the current best available value of the Avogadro constant, we obtain k = 1.380 648 78(83) × 10-23 J·K-1 with u(k)/k = 0.60 × 10-6, where the uncertainty u is one standard uncertainty corresponding to a 68% confidence level. This value is consistent with our previous determinations and with that of the 2014 CODATA adjustment of the fundamental constants (Mohr et al 2016 Rev. Mod. Phys. 88 035009), within the standard uncertainties. We combined the present values of k and u(k) with earlier values that were measured at LNE. Assuming the maximum possible correlations between the measurements, (k present/〈k〉 - 1) = 0.07 × 10-6 and the combined u r (k) is reduced to 0.56 × 10-6. Assuming minimum correlations, (k present/〈k〉 - 1) = 0.10 × 10-6 and the combined u r (k) is reduced to 0.48 × 10-6.
My botty best at summarizing from Wikipedia: the Boltzmann constant (kB or k) is a physical constant . it relates the average relative kinetic energy of particles in a gas with the temperature of the gas . as part of the 2019 red the Boltzmann constant is defined to be exactly 1.3806491023 J/K . this definition allows the temperature unit (in SI system: the kelvin) to be redefined in terms of mechanical units introducing the Boltzmann constant transforms the ideal gas law into an alternative form: p V = N k T . for n = 1 mol, N is equal to the number of particles in one mole root-mean-square speeds found at room temperature accurately reflect this . range from 1370 m/s for helium, down to 240 m . m for xenon . average translational the translational motion velocity vector v has three degrees of freedom . gives the average energy per degree of freedom equal to one third of that, i.e. 1/2kT . quantum mechanical limits on the availability of excited states at the relevant thermal energy per molecule . Arrhenius equation in chemical kinetics takes central importance . central idea of statistical mechanics is inscribed on Boltzmann’ rescaled dimensionless entropy in microscopic terms such that S ′ = ln W , S′= d Q k T . displaystyle the characteristic energy kT is thus the energy required to increase the rescaled entropy by one nat . at room temperature 300 K (27 °C; 80 °F), VT is approximately the thermal voltage is also important in plasmas and electrolyte solutions (e.g. the Nernst equation) it provides a measure of how much the spatial distribution of electrons or ions is affected by “peculiar state of affairs” is illustrated by reference to one of the great scientific debates of the time . a great number of methods have been discovered for measuring the mass of a molecule . in 2017, the the small numerical value of the Boltzmann constant in SI units means a change in temperature by 1 K only changes a particle’s energy by a small amount . the characteristic energy kT is a term encountered in physics research another definition is often encountered in setting k to unity, resulting in the Planck units or natural units for temperature and energy . in this context temperature is measured effectively in units of energy and the Boltzmann
