Thermodynamics in introductory physics typically begins with the ideas of temperature and heating and with the first law of thermodynamics. Then the more difficult parts come: entropy and the second law of thermodynamics. This second portion of the course can begin with a microscopic conception of entropy and a qualitative idea of how thermal systems evolve. The key concept is the ‘‘multiplicity of a macrostate:’’ the number of microstates associated with a macrostate. Starting from these notions—a point of departure and a concept—this paper develops the second law of thermodynamics, the relationship ΔS≥(energy input by heating)/T, and the Carnot efficiency. Offer the entire development both as a specific alternative to what appears in typical introductory texts and as a contribution to a continuing discussion of how to teach thermodynamics to various college audiences.

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