A Carnot's engine is made to work between 2000C and OoC first and then between 00C and -2000C. The ratio of efficiencies of the engine in the two cases is
1 : 73 . 1
1 : 1.73
1 : 1
1 : 2
In first case η1 = 1- T2T1 = 1-(273+0)(273+200) = 200473
In second case η2 = 1-(273-200)(273+0) = 200273
⇒η1η2 = 1(473273) = 1 : 1 . 73