A car engine operates on a Carnot cycle between a high-temperature reservoir at 500 K and a cold reservoir at 300 K. What is the theoretical maximum thermal efficiency of this engine?
Answer and explanation
Correct answer: C. 40%
- Step 1: State the Carnot efficiency formula: eta = 1 - (T_cold / T_hot) where temperatures are in Kelvin.
- Step 2: Substitute given values: eta = 1 - (300 / 500) = 1 - 0.60 = 0.40.
- Step 3: Express as a percentage: 40%.
Answer
40%.
Why not the others: '60%' is the ratio T_cold / T_hot (fraction of heat discarded); '20%' subtracts 300 from 500 and divides by 1000; '50%' is an arbitrary midpoint.
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