Name: kelvin temperature and gas thermometer standards
Uploaded: 2023-04-30T12:29:16.000Z
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Gas Thermometers and the Kelvin Scale

Un thermomètre à gaz évalue la température en fonction des changements de pression ou de volume du gaz rempli.
Il existe deux types de thermomètres à gaz : à volume constant et à pression constante, et le thermomètre à gaz à volume constant est le plus largement utilisé.
Le principe de ce thermomètre est qu’à volume constant, la pression d’un gaz augmente à mesure que la température augmente.
Pour calibrer le thermomètre à gaz, la pression à 0 et 100 degrés Celsius est mesurée.
Ces valeurs sont tracées en ligne droite, qui est extrapolée pour trouver la température de pression zéro.
Cette température est le point zéro de l’échelle Kelvin. Il s’agit de l’échelle standard de température, car l’unité SI de température est Kelvin.
Le zéro absolu est la température la plus basse possible qui reflète idéalement l’absence totale d’énergie thermique.
Sur l’échelle Kelvin, le point de congélation de l’eau est de 273,15, tandis que le point d’ébullition est de 373,15. La différence est la même que sur l’échelle Celsius ; Seul le point zéro est différent.
Ainsi, la relation entre les échelles Kelvin et Celsius peut être facilement établie.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web]. Récupéré de <a href="https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales">https://openstax.org/books/university-physics-volume-2/pages/1-2-thermometers-and-temperature-scales</a></li>
</ol>

les thermomètres à gaz et l'échelle kelvin

La définition de la température en termes de mouvement moléculaire suggère qu'il devrait exister une température minimale possible, où l'énergie cinétique moyenne des molécules est nulle (ou le minimum permis par la mécanique quantique). Des expériences confirment l'existence d'une telle température, appelée zéro absolu. Une échelle de température absolue est celle dont le point zéro est le zéro absolu. De telles échelles sont pratiques en science car plusieurs grandeurs physiques, telles que le volume d'un gaz idéal, sont directement liées à la température absolue.

L'échelle Kelvin est l'échelle de température absolue couramment utilisée en science.

L'échelle Kelvin fait partie du système international d'unités, donc sa définition réelle est plus compliquée que celle donnée ci-dessus. Tout d'abord, elle n'est pas définie en termes des points de congélation et d'ébullition de l'eau, mais en termes du point triple. Le point triple est la combinaison unique de température et de pression à laquelle la glace, l'eau liquide et la vapeur d'eau peuvent coexister de manière stable. La température du point triple est définie comme étant de 273,16 K. Cette définition a l'avantage que bien que la température de congélation et la température d'ébullition de l'eau dépendent de la pression, il n'y a qu'une seule température du point triple.

Même avec des points bien définis sur l'échelle, les différents thermomètres donnent des résultats légèrement différents pour d'autres températures. Par conséquent, un thermomètre standard est nécessaire. Les métrologistes ont choisi le thermomètre à gaz à volume constant à cet effet. Un récipient de volume constant rempli de gaz est soumis à des variations de température et la température mesurée est proportionnelle à la variation de pression. Les résultats dépendent quelque peu du choix du gaz, mais plus le gaz dans le bulbe est peu dense, meilleurs sont les résultats pour différents gaz. Si les résultats sont extrapolés à une densité nulle, les résultats s'accordent assez bien, la pression nulle correspondant à une température de zéro absolu. Les thermomètres à gaz à volume constant sont volumineux et atteignent lentement l'équilibre, ils sont donc principalement utilisés comme références pour étalonner d'autres thermomètres.

Les thermomètres à gaz et l'échelle Kelvin

La définition de la température en termes de mouvement moléculaire suggère qu’il devrait y avoir une température la plus basse possible, où l’énergie cinétique moyenne ...

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kelvin temperature and gas thermometer standards

Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature.

The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling points. Instead, it is tied to the triple point of water. The triple point is the only temperature and pressure combination where ice, liquid water, and water vapor can all coexist. Its temperature is defined as 273.16 K, which is useful because it does not change with pressure the way water’s freezing and boiling points do.

Even with fixed reference points, different thermometers can give slightly different readings for other temperatures. For that reason, scientists need a standard thermometer. Metrologists use the constant-volume gas thermometer for this job. In this device, a gas in a sealed vessel stays at the same volume while temperature changes, and the temperature is found from the change in pressure.

The choice of gas can affect the results a little. However, the less dense the gas in the bulb, the better different gases agree. When the results are extrapolated to zero density, they match well, and zero pressure corresponds to absolute zero. Constant-volume gas thermometers are large and slow to reach equilibrium, so they are mainly used as standards to calibrate other thermometers.

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Kelvin Temperature and Gas Thermometer Standards

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