T–S Diagram (Carnot)
Carnot rectangle — area = work done.
Key Notes
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.
Formulas
Heat absorbed
Area under T-S curve.
Entropy change (reversible)
Definition of entropy.
Adiabatic = isentropic (reversible)
Reversible adiabatic: vertical line on TS.
Carnot cycle area
Carnot rectangle on TS diagram.
Important Points
T-S diagrams show heat flow visually (area under curve).
Isothermal: horizontal. Reversible adiabatic: vertical.
Cycle on TS: clockwise = engine (Q > 0 net, area encloses heat absorbed).
Carnot cycle is a RECTANGLE on TS — easiest place to compute efficiency.
Real processes are IRREVERSIBLE — S of universe increases (2nd law).
TS diagrams used heavily in steam engine and refrigeration design.
T–S Diagram (Carnot) notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.