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Why is it impossible for even a Carnot engine to achieve 100% efficiency?

1. radiation losses cannot be completely stopped
2. perfect heat reservoirs are not available
3. absolute zero temperature cannot be attained
4. friction cannot be entirely removed

Correct answer: absolute zero temperature cannot be attained

Solution

A Carnot engine operates between two temperature reservoirs, and achieving 100% efficiency would require the cold reservoir to be at absolute zero, which is unattainable according to the third law of thermodynamics.

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