Question

The Carnot cycle of a reversible heat engine consists of:

• A. one isothermal and two adiabatic processes
• B. two isothermal and one adiabatic processes
• C. two isothermal and two adiabatic processes
• D. two isobaric and two isothermal processes
• E. two isochoric and two adiabatic processes

Answer 1

The correct option is C two isothermal and two adiabatic processes

The Carnot cycle has the greatest efficiency possible of an engine (although other cycles have the same efficiency) based on the assumption of the absence of incidental wasteful processes such as friction, and the assumption of no conduction of heat between different parts of the engine at different temperatures.

The Carnot cycle consists of the following four processes:

1. A reversible isothermal gas expansion process. In this process, the ideal gas in the system absorbs $q_{in}$ amount heat from a heat source at a high temperature $T_h$, expands and does work on surroundings.
2. A reversible adiabatic gas expansion process. In this process, the system is thermally insulated. The gas continues to expand and do work on surroundings, which causes the system to cool to a lower temperature, $T_l$.
3. A reversible isothermal gas compression process. In this process, surroundings do work to the gas at $T_l$, and causes a loss of heat, $q_{out}$.
4. A reversible adiabatic gas compression process. In this process, the system is thermally insulated. Surroundings continue to do work to the gas, which causes the temperature to rise back to $T_h$.