Name: kelvin temperature and gas thermometer standards
Uploaded: 2023-04-30T12:29:16.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.13

CHEM.13.D

Gas Thermometers and the Kelvin Scale

Un termometro a gas valuta la temperatura in base alle variazioni di pressione o volume del gas riempito.
Esistono due tipi di termometri a gas: a volume costante e a pressione costante, e il termometro a gas a volume costante è il più utilizzato.
Il principio di questo termometro è che, a volume costante, la pressione di un gas aumenta all'aumentare della temperatura.
Per calibrare il termometro a gas, viene misurata la pressione a 0 e 100 gradi Celsius.
Questi valori vengono tracciati in linea retta, che viene estrapolata per trovare la temperatura a pressione zero.
Questa temperatura è il punto zero della scala Kelvin. Questa è la scala standard per la temperatura, poiché l'unità di misura della temperatura SI è Kelvin.
Lo zero assoluto è la temperatura più bassa possibile che riflette idealmente la totale assenza di energia termica.
Sulla scala Kelvin, il punto di congelamento dell'acqua è 273,15, mentre il punto di ebollizione è 373,15. La differenza è la stessa della scala Celsius; solo il punto zero è diverso.
Pertanto, la relazione tra le scale Kelvin e Celsius può essere facilmente stabilita.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Estratto da <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>

termometri a gas e scala kelvin

La definizione di temperatura in termini di movimento molecolare suggerisce che dovrebbe esserci un temperatura più bassa possibile, dove l'energia cinetica media delle molecole è zero (o il minimo consentito dalla meccanica quantistica). Gli esperimenti confermano l'esistenza di tale temperatura, chiamata zero assoluto. Una scala di temperatura assoluta è una in cui il punto zero è lo zero assoluto. Tali scale sono convenienti nella scienza perché diverse quantità fisiche, come il volume di un gas ideale, sono direttamente correlate alla temperatura assoluta.

La scala Kelvin è la scala della temperatura assoluta che è più comunemente usata in scienza.

La scala Kelvin è parte del sistema di unità dell'SI, quindi la sua effettiva definizione è più complicata di quella data precedentemente. Prima di tutto, non è definita in termini di punti di congelamento ed ebollizione dell'acqua, ma in termini di punto triplo. Il punto triplo è la combinazione unica di temperatura e pressione a cui il ghiaccio, l'acqua liquida, e il vapore acqueo possono coesistere stabilmente. Il punto triplo di temperatura è definito come 273.16 K. Questa definizione ha il vantaggio che nonostante la temperatura di congelamento e di ebollizione dipendano dell'acqua dipendano dalla pressione, c'è solo una temperatura del triplo punto.

Anche con punti ben definti sulla scala, termometri diversi forniscono risultati leggermente diversi per altre temperature. Pertanto, viene richiesto un termometro standard. I meteorologi per questo scopo hanno scelto il termometro a gas volume-costante. Un recipiente di volume costante riempito con gas è soggetto al cambiamento di temperatura, e la temperatura misurata è proporzionale al cambiamento nella pressione. I risultati dipendono in qualche modo dalla scelta del gas, ma meno denso è il gas nel bulbo, migliori sono i risultati che concordano per gas diversi. Se i risultati sono estrapolati a densità zero, concordano abbastanza bene, con la pressione zero corrispondente alla temperatura dello zero assoluto. I termometri a gas volume-costante sono grandi e vanno in equilibrio lentamente, quindi sono usati per lo più come standard per calibrare i termometri.

Termometri a gas e scala Kelvin

La definizione di temperatura in termini di moto molecolare suggerisce che dovrebbe esserci una temperatura più bassa possibile, dove l'energia cinetica media ...

Education

Didattica

JoVE Core

Physics

Fisica

Unit 1

Unità 1

Temperature and Heat

Temperatura e Calore

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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.

Kelvin Temperature and Gas Thermometer Standards

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Learn how the Kelvin scale is tied to absolute zero, the triple point of water, and constant-volume gas thermometers used to calibrate other thermometers.

Kelvin Temperature and Gas Thermometer Standards | JoVE K12

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Kelvin Temperature and Gas Thermometer Standards

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