Name: net work in a cyclic thermodynamic process
Uploaded: 2023-04-30T12:31:42.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Physics

2.2.1 9P.2.2.1.1

Cyclic Processes And Isolated Systems

Un système qui n’échange pas de chaleur et ne travaille pas sur son environnement est appelé un système isolé. La variation de l’énergie interne pour de tels systèmes est nulle.
Dans les systèmes non isolés, l’énergie interne ne peut être constante que si le processus suivi est cyclique.
Supposons qu’un système thermodynamique, comme l’air à l’intérieur des poumons, à la pression et au volume initiaux, se dilate jusqu’à un nouvel état final, retourne à son état initial dans un processus thermodynamique. Un tel processus est appelé processus cyclique. 
Dans ce processus, l’énergie interne du gaz reste constante, par conséquent, le travail effectué est égal au transfert de chaleur net.
Dans un diagramme pV, un tel processus cyclique est représenté par un chemin fermé. Supposons que le travail effectué le long du premier chemin soit W1 et que le travail effectué le long du deuxième chemin soit W2. Le réseau effectué dans un processus cyclique est représenté par l’aire entre ces deux chemins fermés.
Il est positif si le processus suit un cycle dans le sens des aiguilles d’une montre et négatif lorsqu’il suit un cycle dans le sens inverse des aiguilles d’une montre.

<ol>
	<li>Young, H. D, et Freedman, R.A. (2012). La physique universitaire avec la physique moderne. San Francisco, Californie : Pearson. p. 633.</li>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web]. pp 125 Tiré de <a href="https://openstax.org/books/college-physics/pages/15-2-the-first-law-of-thermodynamics-and-some-simple-processes">https://openstax.org/books/college-physics/pages/15-2-the-first-law-of-thermodynamics-and-some-simple-processes</a></li>
</ol>

les processus cycliques et les systèmes isolés

Un système thermodynamique sans échange de chaleur et de travail est un système isolé. Pour ces systèmes, l'énergie interne reste constante.

Dans le cas d'un système non isolé, le changement d'énergie interne est nul uniquement si le processus est cyclique. Un processus thermodynamique est considéré comme cyclique si le système subit une série de changements et revient à son état initial.

Considérons un processus cyclique qui revient à son état initial en passant par quatre étapes. Le transfert de chaleur le long de chaque chemin est de 40 J, -80 J, -20 J et 100 J. Quel est le travail net effectué pour ce processus?

Les quantités connues sont le transfert de chaleur pour chaque étape. La quantité inconnue est la quantité nette de travail effectué pour ce processus cyclique.

Selon la première loi de la thermodynamique, le changement d'énergie interne du système est la différence entre le transfert net de chaleur dans le système et le travail net effectué par le système. Étant donné que le changement d'énergie interne est nul, la quantité nette de travail effectué est égale au transfert net de chaleur. Le transfert net de chaleur est la somme du transfert de chaleur pour chaque chemin, soit 40 J. Par conséquent, le travail net effectué est de 40 J.

Le travail net positif effectué implique que le travail effectué par le système est supérieur au travail effectué sur le système. L'énergie thermique fournie au système est utilisée par le système pour effectuer le travail externe.

Les processus cycliques et les systèmes isolés

Un système thermodynamique sans échange de chaleur et sans travail est un système isolé. Pour ces systèmes, l’énergie interne reste constante.
Dans le cas d’un ...

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Physique

Unit 1

Unité 1

The First Law of Thermodynamics

Le premier principe de la thermodynamique

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

net work in a cyclic thermodynamic process

A cyclic thermodynamic process returns a system to its initial state. In a cycle, the change in internal energy is zero. An isolated system is different because it has zero heat exchange and zero work, so its internal energy stays constant.

For a non-isolated system, the internal energy change is zero only when the process is cyclic. The first law of thermodynamics relates internal energy, heat transfer, and work. It states that the change in internal energy is the difference between the net heat transferred into the system and the net work done by the system.

The example here uses a four-step cyclic process. The heat transfer along the four paths is 40 J, -80 J, -20 J, and 100 J. The question is to find the net work done for the full cycle. The net heat transfer is the sum of the heat for each step, which is 40 J.

Because the process is cyclic, the change in internal energy is zero. That means the net work done equals the net heat transfer. So the net work done is 40 J. This positive value means the system does more work than work done on it. The heat energy supplied to the system is used to do external work.

Net Work in a Cyclic Thermodynamic Process

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thermodynamic systems

Open, Closed, and Isolated Systems

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How Internal Energy Changes in Gas Systems

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Isothermal Expansion and Heat Transfer

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Constant Volume and Pressure in Thermodynamics

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Gas Temperature Changes in Adiabatic Processes

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Free Expansion: Pressure, Volume, and Temperature

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key terms and concepts

Learn how the first law of thermodynamics applies to a cyclic process and how to find net work from heat transfer when internal energy stays constant.

Net Work in a Cyclic Thermodynamic Process | JoVE K12

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Net Work in a Cyclic Thermodynamic Process

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