For which combination of working temperatures, the efficiency of Carnot's engine is the least?

Step-by-step solution

We know that, η = 1 - T L T H × 100 When T L = 80   K and T H = 100   K , η = 1 - 80 100 × 100 η = 20 100 × 100 = 20 % When T L = 20   K and T H = 40   K , η = 1 - 20 40 × 100 η = 20 40 × 100 = 50 % When T L = 60   K and T H = 80   K , η = 1 - 60 80 × 100 η = 20 80 × 100 = 25 % When T L = 40   K and T H = 60   K , η = 1 - 40 60 × 100 η = 20 60 × 100 = 33 . 33 %