The P-V and ln P – ln V diagrams

During a reversible transformation, the pressure and volume of the gas are well defined at every instant: the transformation becomes a curve in a plane. In ordinary coordinates $(V, P)$ each process has a characteristic shape; switching to logarithmic coordinates $(\ln V, \ln P)$ the same curves straighten out into straight lines with distinctive slopes. This section shows how to read both diagrams and why the final state alone is not enough to determine the heat and work exchanged.

• La curva nel piano P-V
• Il diagramma ln P – ln V
• Stesso gas, due trasformazioni diverse