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Physics · University

Carnot upper-bound efficiency

Temperatures must be absolute. This is the reversible upper bound between two reservoirs, not a claim about a real engine.

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Method and conditions

Temperatures must be absolute. This is the reversible upper bound between two reservoirs, not a claim about a real engine.

η = 1 − Tc/Th

Worked examples

A reversible heat engine works between 270 K and 710 K. Find its Carnot efficiency as a percentage. Round the final result to 4 decimal places if needed. Answer in %.

η = 1 − 270/710. Multiply the fraction by 100 for percent.

61.9718 %

A reversible heat engine works between 360 K and 520 K. Find its Carnot efficiency as a percentage. Round the final result to 4 decimal places if needed. Answer in %.

η = 1 − 360/520. Multiply the fraction by 100 for percent.

30.7692 %

Try it

  1. A reversible heat engine works between 390 K and 890 K. Find its Carnot efficiency as a percentage. Round the final result to 4 decimal places if needed. Answer in %.

  2. A reversible heat engine works between 370 K and 850 K. Find its Carnot efficiency as a percentage. Round the final result to 4 decimal places if needed. Answer in %.

Check your work

Answers and marking notes
  1. 56.1798 %

    η = 1 − 390/890. Multiply the fraction by 100 for percent.

  2. 56.4706 %

    η = 1 − 370/850. Multiply the fraction by 100 for percent.

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