Carnot Efficiency (η = 1 - T₂/T₁)
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η = 1 - T₂/T₁
What each symbol means
| Symbol | What it stands for |
|---|---|
| η | Efficiency of Carnot engine (dimensionless, 0 < η < 1) |
| T₁ | Temperature of hot reservoir (K) — MUST be in Kelvin |
| T₂ | Temperature of cold reservoir (K) — MUST be in Kelvin |
When to use this
Maximum possible efficiency for ANY heat engine operating between temperatures T₁ and T₂. Real engines always have η < η_Carnot. η = 1 only if T₂ = 0 K (impossible by Third Law). η = 0 if T₁ = T₂. MUST use Kelvin — using °C gives completely wrong answer. Also: η = W/Q₁ = (Q₁−Q₂)/Q₁.