What characterizes a cyclic process?

A cyclic process is characterized by a system returning to its initial state after completing a series of thermodynamic changes. This means that all properties of the system, such as pressure, volume, and temperature, return to their original values at the end of the process. This characteristic is particularly significant in thermodynamics because it allows for the analysis of engines and refrigerators, which operate in cycles to transfer energy efficiently.

In cyclic processes, while the system undergoes various transformations that may involve work and heat exchange, the overall net effect on the system's internal energy and state variables results in it returning to where it started. This fundamental concept also implies that in a complete cycle, the work done by the system equals the heat absorbed (or rejected), reinforcing the principles of energy conservation.

The other options do not accurately represent the defining features of a cyclic process. Specifically, the continuous addition of energy, the notion of only heat exchange without work, and the idea of a permanent change in the system all describe different types of thermodynamic processes that do not reflect the essence of a cycle wherein the system ultimately returns to its initial conditions.