Class 11 Physics Chapter 11 Thermodynamics – Revision Notes

Thermodynamics in Class 11 rests on three laws: the zeroth law establishing temperature, the first law balancing heat and work, and the second law limiting how efficient any engine can be. This chapter also separates isothermal, adiabatic, isochoric, and isobaric processes and works through Carnot efficiency.

Last Updated: September 23, 2026

Laws

• Zeroth law: defines temperature via thermal equilibrium.
• First law: ΔQ=ΔU+ΔW.
• Second law: heat doesn’t spontaneously flow cold→hot; no 100% efficient engine.

Processes

• Isothermal (ΔU=0), Adiabatic (ΔQ=0), Isochoric (ΔW=0), Isobaric (constant P).

Heat Engines

• η=1−Q2/Q1; Carnot: η=1−T2/T1.

One-Line Summary

Thermodynamics governs energy exchange as heat and work, with the first law conserving energy and the second law restricting the direction of spontaneous heat flow and limiting engine efficiency.

Quick visual: a worked diagram from the full Solutions page, for reference.

Frequently Asked Questions

What is the difference between an isothermal and an adiabatic process?
In an isothermal process, the temperature remains constant while heat is exchanged with the surroundings, whereas in an adiabatic process, no heat is exchanged at all, and any change in internal energy comes purely from work done.

What does the Second Law of Thermodynamics say about the direction of natural processes?
The Second Law states that heat cannot spontaneously flow from a colder body to a hotter body without external work being done, which explains why natural processes have a preferred direction and why no engine can be perfectly efficient.

Written by Satish

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