Carnot efficiency is the maximum thermal efficiency for a reversible heat engine between two fixed-temperature reservoirs.
Difficulty
Intermediate
Read time
5 min
Prerequisites
Basic algebra, consistent units, and the stated model assumptions
Source
OpenStax, College Physics 2e, §15.4 (Paul Peter Urone and Roger Hinrichs)OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.
Carnot efficiency is the maximum thermal efficiency for a reversible heat engine between two fixed-temperature reservoirs. Real engines operating between those temperatures cannot exceed it.
| Symbol | Meaning | Units |
|---|---|---|
| Efficiency (carnot) | ||
| Cold-reservoir absolute temperature | ||
| Hot-reservoir absolute temperature |
Find the reversible efficiency bound.
Compare theoretical limits at different temperatures.
Find the Carnot efficiency as a fraction for hot and cold reservoirs at 500 K and 300 K.
OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.
Assumptions
FormuLab is a study reference. Verify formulas, units, assumptions, and course-specific conventions before relying on them.
© 2026 FormuLab. All rights reserved.