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Physics 1220/1320

This comprehensive chapter explores thermodynamics and electromagnetism, focusing on ideal gas behavior and phase diagrams. It delves into phase transitions, including the expansion of ideal gases into real gases, and covers key concepts such as quasi-static processes, the first and second laws of thermodynamics, and the efficiency of heat engines. Additionally, it provides a graphical representation of state functions and examines reversible versus irreversible processes, encapsulating the fundamental principles that govern thermal dynamics and energy conservation.

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Physics 1220/1320

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  1. Physics 1220/1320 Thermodynamics & Electromagnetism Chapter 19 -20

  2. Ideal Gas: Phase Diagram: Substance expanding on melting

  3. Ideal Gas to real gas: Phase transitions Here: liquid/gas

  4. Phase diagrams – 3-dim pVT system

  5. Examples of quasi-static processes: isothermal constant T isobaric constant p isochoric constant V adiabatic no heat flow

  6. 1st Law of Thermodynamics Conservation of energy:

  7. State Functions

  8. Graphical representation of quasi-static processes

  9. State Functions Ideal gas - Isothermal processes

  10. g = Cp/Cv= (5/2R)/(3/2R)=5/3

  11. TVg-1 = const.

  12. Second Law of Thermodynamics: gives direction to processes No system can undergo a process where heat is absorbed and convert the heat into work with the system ending in the state where it began: No perpetuum mobile.

  13. Heat engines: heaters and refrigerators b/c heat cannot flow from a colder to a hotter body w/o a cost (work). iow e=100% is not possible! Reversible vs irreversible processes.

  14. Early heat engines:

  15. 4 stroke or Otto engine intake stroke compression stroke ignition power stroke exhaust stroke Bottom right Ta, bottom left Tb Use T*Vg-1 = const. law for the two adiabatic processes For r=8, g = 1.4 e=56%

  16. Diesel Cycle Typical rexp ~ 15, rcomp ~ 5

  17. Carnot Cycle The best-efficiency cycle 2 reversible isothermal and 2 reversible adiabatic processes.

  18. There are many other useful state functions: the thermodynamic potentials Enthalpy H = U + PV Free energy at const P, T G = U + PV - TS Free energy at const. T F = U – TS Entropy S etc. The first law revised (for a p-V-T system): DU= TdS - pdV

  19. Entropy: Cost of Order – macroscopic interpretation: reversible and irreversible processes Total entropy change zero: reversible Use dQ = S dT in first law!

  20. Entropy ~ microscopic interpretation w is no. of possible states

  21. The 3rd Law of Thermodynamics 3rd Law: It is impossible to reach absolute zero.

  22. ‘Fun’ mnemonic about thermodynamic laws: 1st Law ‘You can’t win, you can only break even’ 2nd Law ‘You can break even only at absolute zero’ 3rd Law ‘You cannot reach absolute zero’ Moral: one can neither win nor break even The American Scientist , March 1964, page 40A The laws of thermodynamics give processes a direction

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