UY1: Isothermal Process



In an isothermal process, the temperature of the system is unchanged. (ΔT = 0). For this process, the first law gives ΔE = 0, thus Q = -W.

This means that the net heat input into the system equals to the net work output by the system.

isothermal

From the ideal gas equation, P1V1 = P2V2 = nRT (isotherm).

Isothermal work done by the gas,

$$\begin{aligned} W_{\text{out}} &= \int\limits_{V_{i}}^{V_{f}} P \, dV \\ &= \int\limits_{V_{i}}^{V_{f}} \frac{nRT}{V} \, dV \\ &= nRT \, \text{ln} \, \frac{V_{f}}{V_{i}} \end{aligned}$$

Note: Since PV = constant, the area of red rectangle = green rectangle. This geometric property will be useful to solve heat cycle problems.

 

Next: Adiabatic Process

Previous: Concept of heat engines and heat pumps

Back To Thermodynamics


Back To Thermodynamics (University Year 1 Physics)

Back To University Year 1 Physics Notes



Mini Physics

Administrator of Mini Physics. If you spot any errors or want to suggest improvements, please contact us. If you like the content in this site, please recommend this site to your friends!



Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.