The Carnot cycle is a theoretical thermodynamic cycle that represents the most efficient possible heat engine operating between two temperature reservoirs. It consists of four reversible processes: two isothermal processes and two adiabatic processes.

1. Isothermal Expansion (Process AB):

   • The working substance (often a gas) is in contact with a high-temperature reservoir (source) at temperature ��TH​.
   • During this process, the gas expands isothermally, absorbing heat ��QH​ from the high-temperature reservoir.
   • Work is done on the surroundings during this expansion.

2. Adiabatic Expansion (Process BC):

   • The gas continues to expand adiabatically, meaning without heat exchange with the surroundings.
   • The temperature of the gas decreases during this expansion.
   • Work is done on the surroundings during this adiabatic expansion.

3. Isothermal Compression (Process CD):

   • The working substance is brought into contact with a low-temperature reservoir (sink) at temperature ��TC​.
   • During this process, the gas is compressed isothermally, releasing heat ��QC​ to the low-temperature reservoir.
   • Work is done on the gas during this compression.

4. Adiabatic Compression (Process DA):

   • The gas undergoes adiabatic compression, increasing its temperature.
   • Work is done on the gas during this adiabatic compression.

The efficiency (�η) of the Carnot cycle is given by the ratio of the work done during the isothermal expansion to the heat absorbed during that process:

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