Three hypothetical heat engines P, Q and R each operate between a single hot reservoir and a single cold reservoir. Their operating temperatures are given below:
Engine P : TH=600K, TC=300K
Engine Q : TH=900K, TC=450K
Engine R : TH=750K, TC=250K
a) Arrange the three engines in the order of their maximum possible (ideal) efficiency without performing any numerical calculation.
b) Give clear reasons for the order you have chosen, quoting the relevant principle of the Second Law.
c) Suppose all three engines are real and therefore irreversible. Explain qualitatively how irreversibility could alter the ranking obtained in part (a).