According to the Second Law, you cannot have a cycle with 100% efficiency.

Study for the EPRI Heat Transfer and Fluid Flow Test. Prepare with flashcards and multiple choice questions, each with hints and explanations. Get ready for your exam!

Multiple Choice

According to the Second Law, you cannot have a cycle with 100% efficiency.

Explanation:
The key idea is that you cannot convert all of the heat you take in into useful work in a cyclic process. The Second Law sets a fundamental limit: some heat must be rejected to the cold reservoir, so the efficiency can never reach 100%. In fact, the Carnot bound shows the maximum possible efficiency is η = 1 − Tc/Th, which is always less than 1 for any finite temperatures Th and Tc. So 100% efficiency is impossible. Choosing the option that states 100% efficiency reflects that impossibility. The other numbers don’t capture the core limit: 200% would violate energy conservation, and 50% or 0% can be realized in various cycles under the right conditions (0% is a degenerate case of no work produced).

The key idea is that you cannot convert all of the heat you take in into useful work in a cyclic process. The Second Law sets a fundamental limit: some heat must be rejected to the cold reservoir, so the efficiency can never reach 100%. In fact, the Carnot bound shows the maximum possible efficiency is η = 1 − Tc/Th, which is always less than 1 for any finite temperatures Th and Tc. So 100% efficiency is impossible.

Choosing the option that states 100% efficiency reflects that impossibility. The other numbers don’t capture the core limit: 200% would violate energy conservation, and 50% or 0% can be realized in various cycles under the right conditions (0% is a degenerate case of no work produced).

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