What is the primary characteristic of the Carnot cycle?

The primary characteristic of the Carnot cycle is that it adds and rejects heat at constant temperatures. This is a fundamental aspect of the idealized Carnot cycle, which serves as a model for the most efficient heat engine possible. The cycle consists of four reversible processes: two isothermal (constant temperature) processes and two adiabatic (no heat transfer) processes.

During the isothermal expansion phase, the working substance absorbs heat from a high-temperature reservoir while maintaining a constant temperature. Conversely, during the isothermal compression phase, the system releases heat to a low-temperature reservoir, again at a constant temperature. This heat addition and rejection at constant temperatures ensures maximum efficiency according to the second law of thermodynamics.

While other options do mention aspects of thermodynamic cycles, they do not define the Carnot cycle accurately. The Carnot cycle’s efficiency and performance are fundamentally linked to the isothermal processes occurring at constant temperature, setting it apart from other cycles that may operate under different conditions.