A first statement of the second law of thermodynamics concerns the direction heat transfer takes between two bodies at different temperatures. What does this first statement say?
AHeat transfer occurs equally in both directions between bodies
BHeat transfer occurs from cooler to hotter bodies only
CHeat transfer occurs from hotter to cooler bodies only
DHeat transfer depends only on the bodies' relative sizes
Answer & Solution
Correct answer: C. Heat transfer occurs from hotter to cooler bodies only
1. The source's first expression of the second law concerns the natural direction of spontaneous heat transfer.
2. It states that heat transfer occurs spontaneously from higher-temperature bodies to lower-temperature ones, but never spontaneously the other way.
3. This directly rules out option B, which reverses that direction, and option A, which claims no preferred direction exists at all.
4. Relative size of the two bodies is not what determines the direction of spontaneous heat transfer, only their temperature difference is, ruling out option D.
_Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency_
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