Exam-style question
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Describe how the second law of thermodynamics limits the efficiency of heat engines.
Model answer
What a good answer should say
- The second law of thermodynamics limits the efficiency of heat engines by stating that not all heat energy can be converted into work; some energy must be expelled as waste heat.
- This means that the maximum efficiency of a heat engine is determined by the temperature difference between the heat source and the heat sink, preventing 100% conversion of energy.
Explanation
Why this works
This answer is strong because it clearly outlines the limitation imposed by the second law (not all heat can be converted to work) and explains the mechanism (temperature difference between source and sink). It connects the effect (maximum efficiency is limited) to the consequence (prevention of 100% energy conversion).
The question assesses the ability to apply thermodynamic concepts.
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