What cycle process has constant entropy?

What cycle process has constant entropy?

• A. Isotropic Process
• B. Isentropic Process
• C. Isobaric Process
• D. Isothermal Process

Answer: (A)

The key idea is entropy staying the same during a process. When a process is reversible and adiabatic—no heat flows in or out and no irreversibilities occur—the entropy does not change, so the process is isentropic. In a cycle, an isentropic step means the system’s state changes without generating or absorbing entropy, and for an ideal gas this leads to the relationship PV^γ = constant (or TV^{γ−1} = constant), reflecting how pressure, volume, and temperature adjust while S remains fixed. The other terms don’t guarantee constant entropy. Isotropic focuses on uniform properties in all directions, not energy or entropy changes. Isobaric means pressure is constant, but heat transfer can still occur and entropy may change. Isothermal means temperature is constant, yet entropy typically changes with volume (for a gas, S depends on both T and V), so entropy isn’t generally constant.

The key idea is entropy staying the same during a process. When a process is reversible and adiabatic—no heat flows in or out and no irreversibilities occur—the entropy does not change, so the process is isentropic. In a cycle, an isentropic step means the system’s state changes without generating or absorbing entropy, and for an ideal gas this leads to the relationship PV^γ = constant (or TV^{γ−1} = constant), reflecting how pressure, volume, and temperature adjust while S remains fixed.

The other terms don’t guarantee constant entropy. Isotropic focuses on uniform properties in all directions, not energy or entropy changes. Isobaric means pressure is constant, but heat transfer can still occur and entropy may change. Isothermal means temperature is constant, yet entropy typically changes with volume (for a gas, S depends on both T and V), so entropy isn’t generally constant.