1. Example of a Spring Wind in Lubbock, Texas!

2. Ch. 4: Macroscopic Parameters & Measurement: Classical Thermo, Part I

3. Laws of Thermodynamics: Overview 0 th Law: Defines Temperature (T) Allows the use of Thermometers! 1 st Law: Defines Energy & Says Energy is Conserved. Also Defines Internal Energy Ē Heat Q Mechanical Work W

4. 2 nd Law: Defines Entropy (S) 3 rd Law: Gives Entropy a Numerical Value (at low T!) NOTE! These laws are UNIVERSALLY VALID for systems at equilibrium. They can’t EVER be circumvented for such systems!

5. Chapters 4 & 5: In these chapters, we will have a Purely Macroscopic Physics Discussion of the consequences of The 4 Laws of Thermo!

6. The Ch. 4 focus is on measurements of various macroscopic parameters: Work (W) Internal Energy (Ē) Heat (Q) Temperature (T) Entropy (S)

7. Sect. 4.1: Work (W) & Internal Energy (Ē) From Classical Mechanics, in principle, we know how to measure Macroscopic, Mechanical Work (W): Simply put, such a measurement would change an external parameter x of the system & observe the resulting change in the mean generalized force. (In what follows, Make the Replacement → X(x)). For a quasi-static, infinitesimal change, the infinitesimal work done is defined as: đW = X(x)dx.

8. For a quasi-static, infinitesimal change, the infinitesimal work done is defined as: đW = X(x)dx. Then, from the observed change in X(x) as a function of x, the macroscopic work done is the integral: W = ∫ đW = ∫ X(x)dx. Limits: x i → x f, where x i & x f are the initial & final x in the process. Of course, as we’ve discussed, The Work W Depends on the Process (depends on the path in the X – x plane!).

9. Example: Work Done by Pressure with a Quasi-static Volume Change V i  V f If the volume V is the external parameter, the mean generalized force is the mean pressure = p(V). So, for a quasi-static volume change, the work done is the integral: W = ∫ đW = ∫ p(V)dV The limits are V i → V f.

10. For a quasi-static volume change, the work done is the integral: W = ∫ đW = ∫ p(V)dV The limits are V i → V f. The Work W Depends on the Process (depends on the path in the p – V plane!)

11. Example For a gas in a cylindrical chamber with a piston, The force on the piston is: So, the work W done by the gas in expanding the cylinder from V 1 to V 2 is:

12. This clearly depends on the path taken. The work W done by the gas in expanding the cylinder from V 1 to V 2 is given by the integral: That is, the work W done is equal to the area of the region under the curve in a PV diagram.

13. Question: If a gas is allowed to complete a cycle, has net work been done? The net work W done by a gas in a complete cycle is Equal to the Pink Area of the region enclosed by the path. If the cycle is clockwise on the PV diagram, the gas does positive work.

14. Note: There are many possible ways to take the gas from an initial state i to final state f. The work done W is, in general, different for each. This is consistent with the fact that đW is an inexact differential! Figures (a) & (b) are only 2 of the many possible processes!

15. Figures (c), (d), (e), (f) are 4 more of the many possible processes!

16. Thermodynamics Terminology Process  A change of a system from some initial macrostate to some final macrostate. Path  The intermediate steps in a process between the initial & final macrostates. Isobaric Process  A process at constant pressure: p 1 = p 2 Isochoric Process  A process at constant volume, V 1 = V 2. Section 4.2: Heat (Q): The 1 st Law of Thermodynamics

17. More Thermodynamics Terminology I Isothermal Process  A process at constant temperature, T 1 = T 2 Adiabatic Process  A process with Q = 0 (No heat exchange) Free Expansion Process  A process where Q = W = ΔĒ = 0 Cyclic Process  A process with the initial state = the final state.

18. The 1 st Law of Thermodynamics ΔĒ = Ē f – Ē i = Q – W For an infinitesimal, quasi-static process, this becomes dĒ = đQ - đW So, the mean internal energy Ē of a system tends to increase if energy is added as heat Q & tends to decrease if energy is lost as work W done by the system.

19. Section 4.3: Temperature & Temperature Scales (Ch. 3 Discussion Briefly Revisited!)

20. Temperature Triple Point of Water Constant Volume Gas Thermometer

21. p  Pressure in the gas, C  A constant. p 0  Atmospheric pressure ρ  Density of mercury in the Manometer p 3  Measured gas pressure

22. A gas thermometer temperature is

23. Celsius & Fahrenheit Scales Conversion Between Celsius & Fahrenheit : T C  Celsius Temperature. T  Kelvin Temperature.