According to Carnot Theorem:

"Of all engines working between two given temperature, none is more efficient than a carnot engine."

I want to know what actually is meant by an engine working between two temperatures? Is it always necessary that the engine should follow the Carnot cycle(four path) or would any other number of cyclic processes do the same?

My Answer:
"I think any engine would do the same because in the proof they do not use the fact that the engine (other than carnot) is not necessarily reversible!"

Now need a clarification!

  • $\begingroup$ It means that, whatever the process is (and it doesn't have to be a Carnot process), the engine can exchange heat only with two reservoirs at specified temperatures. $\endgroup$ Jan 12, 2021 at 13:45

1 Answer 1


Heat flows from higher temperature regions to lower temperature regions. A heat engine is a device which extracts useful work from such a heat flow while it is flowing from one region to the other. This is what the "two given temperatures" refers to.

Carnot proved that regardless of the details of the engine's operation, the temperature difference between the hotter source and the colder sink establishes the maximum theoretical efficiency of the engine, which can never be exceeded in actual practice.


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