Heat Engine Efficiency

η = \frac{W}{Q _{H}} = 1 - \frac{Q _{C}}{Q _{H}}

Efficiency of any heat engine.

Variables

η

Efficiency

Work output / Heat input

unitless

W

Work output

Useful work

J

Q_H

Heat input

Heat from hot reservoir

J

Q_C

Heat output

Heat to cold reservoir

J

Derivation

η = W/Q_H. Since W = Q_H - Q_C: η = 1 - Q_C/Q_H.

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