alleryStart learning →What condition would be required for a heat engine to reach 100 percent thermal efficiency?
ANo heat rejected to a cold reservoir
BAn infinite hot reservoir temperature
CZero work output from the engine
DA cold reservoir hotter than the hot reservoir
Answer & Solution
Correct answer: A. No heat rejected to a cold reservoir
1. Efficiency is defined as work output divided by heat input, Eff = W divided by Qh.
2. Efficiency reaches 100 percent only if no heat at all is transferred to the environment, meaning Qc = 0.
3. The second law of thermodynamics rules this condition out for any real heat engine.
4. An infinite hot reservoir temperature, zero work output, or a hotter cold reservoir are not the condition described.
5. So no heat rejected to a cold reservoir is correct.
_Source: OpenStax Physics (CC BY 4.0), Ch 12 "Thermodynamics", section 12.4 Applications of Thermodynamics: Heat Engines, Heat Pumps, and Refrigerators_
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