T–S Diagram (Carnot)

TS diagram: temperature (T) vs entropy (S). Useful complement to PV diagram.

Each point: a thermodynamic state. Each curve: a process.

Isothermal: HORIZONTAL line (T = const).

Adiabatic (reversible): VERTICAL line (S = const, isentropic).

Area under T-S curve = heat absorbed: Q = ∫T·dS.

Cyclic process: closed loop. Enclosed area = net heat absorbed = net work output (for an engine).

Carnot cycle on TS: PERFECT RECTANGLE — two isotherms (horizontal) + two adiabats (vertical).

TS diagram makes 2nd law of thermodynamics visually direct: entropy can only stay constant (reversible) or increase.