How is an isobaric process represented in a pressure vs. volume graph?

In a pressure vs. volume graph, an isobaric process is represented by a horizontal line. This is because an isobaric process is characterized by constant pressure throughout the entire process. As the volume changes—whether it is expanding or compressing—the pressure remains the same.

On the graph, this translates to a horizontal movement along the volume axis while the pressure measurement does not change, resulting in a line that maintains a constant level on the pressure axis. In contrast, a vertical line would indicate that the volume is not changing while the pressure varies, which does not depict an isobaric process. Similarly, a curved line would suggest that the relationship between pressure and volume is not linear, and a sloped line would represent a change in both pressure and volume, indicating a process where at least one of those parameters varies, which again does not fit the definition of an isobaric process.