Final answer:
A heat engine is a system that converts heat energy into mechanical work, with efficiency being a critical parameter in its operation.
Explanation:
A heat engine is a system that converts heat or thermal energy into mechanical work. It operates by extracting heat from a hot reservoir, producing work, and expelling a reduced amount of heat into a cold reservoir. Efficiency, calculated as the useful work extracted divided by the heat input, is crucial for evaluating heat engine performance.
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