Second Law: Entropy & the Carnot Cycle

Module 4 · 4 of 8

🌀Second Law: Entropy & the Carnot Cycle

Why heat flows one way and engines have a ceiling

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Why heat flows one way and engines have a ceiling

The second law introduces entropy — a state function that only increases for the universe. The Carnot cycle makes it concrete: no heat engine between two temperatures can beat the efficiency 1 − Tc/Th, and that bound is pure thermodynamics.

Difficulty

intermediate

Time

~35 min

Equations

Practice Qs

Learning Objectives

✓Define entropy via dS = δq_rev/T and state the second law
✓Compute entropy changes for isothermal ideal-gas processes
✓Derive and apply the Carnot efficiency 1 − Tc/Th
✓Explain the Clausius inequality and irreversibility
✓Relate entropy to the number of microstates (Boltzmann)

Prerequisites

First law & reversible workLogarithms

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