复旦大学：《大学物理——热学》课程教学资源（PPT课件）第15次课

大学物理(热学) 1) Review 2) Carnot's Ideas 3 The Second Law 4) Carnot's cycle 2006-12-13 2021/9/5

2021/9/5 1 大学物理（热学） 1) Review 2) Carnot’s Ideas 3) The Second Law 4) Carnot’s cycle 2006-12-13

(at 1 atm constant ressure s 20c unless otherwise stated) =MC△ SpeciflcⅡeaC kcal/kg ∈ca】/g E /g·C 重num 22 900 Acohol Ethyl) 0.58 2400 Copper 0.093 390 Glass .2O 84o ron or steel O11 45O ead O031 13o Marble O.21 86o Mercury O033 ⊥4o Siver o.056 230 Nood Wate IIce 之1OD 工 IdLc 15°c) 工.00 4186 Stea (10C) O.48 2010 Human body Average) O83 340 Protein 0.4

TABLE 19-3 Specific heats of gases at 15.C Q=nCyAT Specific heats Molar specific heats Q=nCDAT cl/kg·K) (cal/mol K Cp -C y P Gas C C V P (cal/mol K) Monatomic He 0.751.15 2.98497 1.67 e 0.1480.246 2.98497 167 Diatomic 0.1770.248 4966.95 19 1.40 0.1550218503703 2.00 140 Triatomic CO 0.1530.199 680883 2.03 1.30 H2O(100C03500482 6.208.20 2.00 1.32 Polyatomic CH 0.3430.41210.301235 2.05 1.20

Q=nCv⊿T Q=nCp⊿T

AR+Cy FIGURE 19-16 Molar specific heat 3R ydrogen molecules(H,) As the ional kinetic energy I.----ir the translational kinetic energy can 2R Rotational kinetic energy be transferred in collisions into 201500100ld

FIGURE 19-17 Molar heat capacities of solids as a function of temperature eat Beryllium Diamond 2 01002003004005006007008009001000 Temperature(K)

Figure 34.6 temprature heat of normal and conducting aluminum. The normal phase is produced below T, by application of a weak (300-gauss) magnetic tick which d superconducting but has otherwise negligible fect on the specific heat, The Debye temperature is quite high in aluminum. so the specilic hcat is dominated by the clectronic contribution throughout thi range (as can be seen from the fact that the normal-state curve is quite close to be linear). 'The discontinuity at T agrees well with the theo 34.22) ⊥h1」11 Ies-cn/c,=1,43. Well be 1.07 2.0 low T c, drops far belot resting the existence gy gap. (N, E. Phillips, Phys. Rer. 114. 676 1959)

PVEC Isothermal B PVEC Adiabatic . C FIGURE 19-8 PV diagram for adiabatic(AC) and isothermal (AB) processes on an ideal gas

PV=C PV =C

Two uses for a heat engine: a modern coal-burning power plant, and an old steam locomotive. Both produce steam which does work-on turbines to generate electricity, and on a piston that moves linkage to turn locomotive wheels The efficiency of any engine--no matter how carefully engineered-is limited by nature as described in the second law of thermodynamics. This great law is best stated in terms of a quantity called entropy, which is unlike any other. Entropy is not conserved, but instead is constrained always to increase in any real process. Entropy is a measure of disorder. The second 17 law of thermodynamics tells us that as time moves forward. the disorder in the universe increases. We also discuss many practical matters such as heat engines, heat pumps, and refrigeration CHAPTER 20

4+186丁=ca e ca Weight FIGURE 19-1 Joule's experiment on the mechanical equivalent of heat H204s→(S.Sc

瓦特 J. Watt 蒸汽机 James Watt (1736-1819)(Courtesy the E. F. Smith Collection, Van-Pelt-Dietrich Library, University of Pennsylvania)

瓦特 J. Watt 蒸汽机