Question

The process in which no heat is supplied or rejected and entropy is constant is known as:

• A. Polytropic process
• B. Isothermal process
• C. Adiabatic process
• D. Isentropic process

Hint:

An isentropic process is defined as a reversible adiabatic process. It satisfies two conditions:
- No heat transfer (Adiabatic, \(Q = 0\))
- Constant entropy (Isentropic, \(\Delta S = 0\))

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Thermodynamic processes are classified based on the variables (such as pressure, volume, temperature, heat, or entropy) that are held constant during the process.

Step 2: Detailed Explanation:
Let us analyze the definitions of each process listed:
- Polytropic process: A general thermodynamic process described by the relation \(PV^n = C\), where \(n\) is the polytropic index. Heat transfer and entropy changes occur during this process.
- Isothermal process: A process in which the temperature of the system remains constant (\(\Delta T = 0\)). Heat is exchanged with the surroundings to maintain this temperature.
- Adiabatic process: A process in which no heat is transferred into or out of the system (\(Q = 0\)). However, if internal friction or irreversibilities are present, the entropy of the system will increase (\(\Delta S > 0\)).
- Isentropic process: A process that is both adiabatic (\(Q = 0\)) and reversible.
- Since it is reversible and adiabatic, the change in entropy is zero:
\[ dS = \frac{\delta Q_{\text{rev}}}{T} = 0 \]
- Therefore, the entropy of the system remains constant throughout the process.
Thus, a process with no heat transfer and constant entropy is an isentropic process.

Step 3: Final Answer:
The process is known as an isentropic process. Hence, the correct option is (D).