Efficiency of a Carnot engine: Efficiency is defined as the ratio of work done by the working substance in one cycle to the amount of heat extracted from the source.
Applying isothermal conditions, we get,
Here we omit the negative sign. Since we are interested in only the amount of heat (QL) ejected into the sink, we have
Note : TL and TH should be expressed in Kelvin scale.
Important results:
1. η is always less than 1 because TL is less than TH . This implies the efficiency cannot be 100%.
2. The efficiency of the Carnot’s engine is independent of the working substance. It depends only on the temperatures of the source and the sink. The greater the difference between the two temperatures, higher the efficiency.
3. When TH = TL the efficiency η = 0. No engine can work having source and sink at the same temperature.
