A Carnot engine works between $T_h = 400$ K and $T_c = 300$ K. Its efficiency is:
A$50\%$, the simple average shortcut here
B$75\%$, the ratio of cold to hot temperatures
C$33\%$, dividing the difference by cold temperature
D$25\%$, since $\eta = 1 - 300/400 = 0.25$
Answer & Solution
Correct answer: D. $25\%$, since $\eta = 1 - 300/400 = 0.25$
$\eta = 1 - T_c/T_h = 1 - 0.75 = 0.25 = 25\%$.
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