Chapter 11 — Thermodynamics

Chapter 11 of the Class 11 Physics NCERT textbook, "Thermodynamics", deals with heat, temperature, and energy conversion. It studies the laws governing thermal energy transformation between heat and work, exemplified by processes like friction producing heat or steam engines converting heat to work.

• Laws that define temperature and energy — The Zeroth Law grounds the very idea of temperature through thermal equilibrium, while the First Law extends energy conservation to heat, stating that heat supplied equals internal energy change plus work done by the system.
• State variables and thermodynamic processes — Internal energy is a state variable set only by the system's condition, not its history. The chapter surveys key processes—isothermal, adiabatic, isochoric, isobaric, and cyclic—each holding one property fixed as the system changes.
• Limits on converting heat to work — The Second Law reveals that no engine can turn heat fully into work, capping efficiency. The idealised Carnot engine sets the maximum theoretical efficiency between hot and cold reservoirs, framing the physics of real heat engines.

1. 01Zeroth Law: two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other; establishes temperature concept
2. 02Heat (energy transfer via temperature difference) and work (energy transfer via other means) are two distinct modes of changing system internal energy
3. 03First Law: ∆Q = ∆U + ∆W states that heat supplied equals internal energy change plus work done by system
4. 04Internal energy is a state variable depending only on system state (pressure, volume, temperature), independent of path taken
5. 05Second Law: no heat engine can achieve 100% efficiency; Carnot engine provides maximum theoretical efficiency of η = 1 − T₂/T₁ between hot (T₁) and cold (T₂) reservoirs
6. 06Adiabatic process: no heat exchange (Q = 0); isothermal process: constant temperature (T fixed); isochoric: constant volume (V fixed); isobaric: constant pressure (P fixed)