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When one leg of the unit is placed in a cup of cold water and one leg is placed in a cup of hot water, some of the thermal energy from the hot water is converted into work by the converter and the fan turns. If the hot and cold water are mixed together in a large container and both legs of the unit are placed in the container, then the fan doesn’t turn.
Since the total energy of the mixed water is the same as the total energy of the unmixed water, there is sufficient energy to turn the fan. However, this would violate the Second Law of Thermodynamics: a transformation whose only final result is to transform into work heat extracted from a source which is at the same temperature throughout is impossible. This can be shown mathematically, proving that no physical process will occur that decreases the entropy of the universe. |
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