• Heat Engine: A device that performs useful work by converting energy to work continuously.
• Carnot Cycle: A cyclic heat engine described by Nicolas Léonard Sadi Carnot in 1824.

• Energy Conversion: Transfers energy Qh at high temperature Th and rejects energy Qc at lower temperature Tc.
• Work Done: Uses the energy difference (Qh − Qc) for work.
• Continuous Cycle: For ongoing work, the engine must return to its starting point in a cycle.

📝 Formula: \(n = \frac {useful work output}{input energy} =\frac {Qh - Qc}{Qh} \)

Real World Example: Think of a sponge. If you squeeze a soaked sponge, the water coming out is Qh. The water left is Qc. The difference is the work you did!

• Step A→B:

  • Isothermal Expansion: Gas absorbs energy Qh at Th.
  • Temperature Remains Same: So, internal energy doesn't change.
  • Work Done: All absorbed energy does work through gas expansion.

  Real World Example: Imagine inflating a balloon. The air inside expands and pushes the balloon's walls outward!

• Step B→C:

  • Adiabatic Expansion: No energy is absorbed or rejected by gas.
  • Internal Energy: Decreases and temperature drops to Tc.
  • Work Done: Gas's internal energy converts to work.

• Step C→D:

  • Isothermal Compression: Gas releases energy Qc. No change in internal energy but gas is compressed.

• Step D→A:

  • Adiabatic Compression: Work done on gas increases its internal energy, returning it to state A.

Reversible Process: The system can return to its prior state with a minuscule change to its properties or surroundings.

• System always stays in a thermodynamic equilibrium.
• For true reversibility, changes must occur infinitely slowly.