Carnot engine efficiency and exhaust problem

[lzh]

Homework Statement

The exhaust temperature of a Carnot heat engine is 121◦C. What is the intake temperature if the efficiency of the engine is 13.4 %? Answer in units of ◦C.

Homework Equations

e=1-(Tc/Th)

The Attempt at a Solution

This seems like just a plug and chug problem:
0.134=1-(121/Th)
Th=139.723 ◦C
However, this answer is wrong-according to my Quest web homework. Am I missing something here? Thanks

 

[alphysicist]

Hi lzh,

Homework Statement

The exhaust temperature of a Carnot heat engine is 121◦C. What is the intake temperature if the efficiency of the engine is 13.4 %? Answer in units of ◦C.

Homework Equations

e=1-(Tc/Th)

The Attempt at a Solution

This seems like just a plug and chug problem:
0.134=1-(121/Th)
Th=139.723 ◦C
However, this answer is wrong-according to my Quest web homework. Am I missing something here? Thanks

The Celsius scale is not a thermodynamic temperature scale. You need to use a temperature scale such as Kelvin here.

 

[lzh]

Oh! I see! Thanks! I got it now!