By which one of the following working temperature the efficiency of a carnot engine obtained maximum ?

Options

A. 100 K , 80 K
B. 80 K , 60 K
C. 40 K , 20 K
D. 60 K , 40 K

Answer

C

Explanation

Efficiency of carnot engine `eta=1-T_2/T_1`
`therefore` For getting maximum efficiency , the ratio of `T_2/T_1` must be minimum .
From option (A) `T_2/T_1=80/100`=0.8
From option (B) `T_2/T_1=60/80=3/4`=0.75
From option (C) `T_2/T_1=20/40=1/2`=0.50
From option (D) `T_2/T_1=40/60 =2/3`=0.67
`therefore` The minimum value of `T_2/T_1` is in (C ) so efficiency obtained maximum