Question

An ideal heat engine exhausting heat at ${77}^{o}C$ is to have a 30% efficiency. It must take heat at :

• A. ${127}^{o}C$
• B. ${227}^{o}C$
• C. ${327}^{o}C$
• D. ${673}^{o}C$

Answer 1

Answer: (B)

${227}^{o}C$

Given,
$\eta =3/10$.
$\eta =1-7/10$
Now as we know efficiency of a carnot engine is given by,
$\eta =1-\left(T_1/T_2\right)$
We have
$T_1/T_2=7/10$
Given
$T_1=350$ K
Substituting values in the equation we have $T_2=500$ K