Efficiency of a Heat Engine

📊 intermediate

$$\eta = 1 - \frac{Q_L}{Q_H}$$

Measures the fraction of heat energy converted into useful work.

Variables & Units

$\eta$

Efficiency

Unit: Ratio (0 to 1)

$Q_H$

Heat absorbed from hot reservoir

Unit: Joule ($J$)

$Q_L$

Heat rejected to cold reservoir

Unit: Joule ($J$)

Key Information

📐 Derived From

First and Second Laws of Thermodynamics.

💡 Example

Engine taking $1000 J$ of heat and outputting $400 J$ of work has $40\%$ efficiency.

🔧 Applications

Automotive engineering and power plants.

⚠️ Constraints

Cannot be $100\%$ efficient due to Second Law.

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