Question

Carnot engine is a reversible engine. It can be proved from the:

• A. Zeroth Law of Thermodynamics
• B. First Law of Thermodynamics
• C. Second Law of Thermodynamics
• D. Third Law of Thermodynamics

Hint:

The Carnot engine’s reversibility (where changes can be reversed back to the starting point), combined with its operation between two constant-temperature heat reservoirs, leads to maximum possible efficiency, meaning it’s the ideal, theoretical scenario, and real-world engines always perform worse. The engine operates in four fully reversible steps: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.

Answer 1

The Correct Option is C

The Carnot engine is a theoretical thermodynamic cycle that is reversible and operates with the maximum possible efficiency. The proof that the Carnot engine is reversible is deeply rooted in the Second Law of Thermodynamics, particularly its implications for entropy changes and the direction of thermodynamic processes. The Second Law states that in a reversible process, the total entropy of an isolated system remains constant (∆S = 0), while irreversible processes lead to an increase in entropy (∆S > 0).
The Carnot cycle is a series of reversible steps. Because each step is reversible, the process can run in reverse and the total change in entropy for the entire cycle is zero. The proof involves showing that no other engine operating between the same two temperatures could be more efficient than the Carnot engine without violating the Second Law. This analysis uses the fact that reversible processes can be reversed without leaving a trace and that if another engine was more efficient the process would violate the Second Law.