Heat and Thermodynamics

9.7 The Thermodynamic or Kelvin Scale of Temperature

We have seen that a Carnot’s engine is made up of a working substance, source and a sink maintained at two different temperatures. We have proved that the efficiency of Carnot's engine is independent of nature of the working substance. It must, therefore, depend only on the temperatures θ₁ and θ₂ of the source and the sink, respectively. Thus, efficiency is

 

 

where W is the work done per cycle and Q₁ is the heat drawn at temperature θ₁ and Q₂ is the heat rejected at temperature θ₂. In other words,

 

 

so that

 

 

Let another Carnot's engine work between temperatures θ₂ and θ₃ (θ₂