# Physics 312 Lecture: "Work done by Thermodynamic Processes" May 7, 1998

• The work done by an engine depends on the precise process by which it converts heat into mechanical power
• Four types of thermodynamic processes are
• isobaric: pressure remains constant
• isochoric: volume remains constant
• isothermal: temperature remains constant
• adiabatic: no heat enters or leaves the system during the change
• One can figure out how much work is done by any process by integrating dW = P*dV during the transition
• The Pressure-Volume (PV) diagram serves to illustrate changes in the properties of a system
• The work done by a process is equal to the area beneath the process' curve in the PV diagram
• Isobaric process does work: W = P (Vf - Vi)
• Isochoic process does work: W = 0
• Isothermal process does work: W = nRT ln(Vf/Vi)
```                        X          1 - gamma        1 - gamma
W =   ---------   (Vf             - Vi         )
1 - gamma

where
gamma
X = P * V               at any point along the curve

```
• The work done by a cyclic process is equal to the area within the closed loop it defines in the PV diagram

This lecture discusses material in Chapter 20 of Serway.