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PHY 341/641 Thermodynamics and Statistical Physics Lecture 3

PHY 341/641 Thermodynamics and Statistical Physics Lecture 3 Introduction to thermodynamics (Chapter 2) Definition of “the system” Thermodynamic variables (T, P, V, N, …) First law of thermodynamics -- the sign of work Some examples for ideal gas systems Some cyclic processes

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PHY 341/641 Thermodynamics and Statistical Physics Lecture 3

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  1. PHY 341/641 • Thermodynamics and Statistical Physics • Lecture 3 • Introduction to thermodynamics (Chapter 2) • Definition of “the system” • Thermodynamic variables (T, P, V, N, …) • First law of thermodynamics -- the sign of work • Some examples for ideal gas systems • Some cyclic processes • Efficiency of process PHY 341/641 Spring 2012 -- Lecture 3

  2. Macroscopic viewpoint – thermodynamics (start reading Chapter 2) System of study Controlling medium PHY 341/641 Spring 2012 -- Lecture 3

  3. Thermodynamic process -- WORK various sign conventions !!!#$#!!! PHY 341/641 Spring 2012 -- Lecture 3

  4. Work sign conventions in various text books: Work done BY the system Work done ON the system PHY 341/641 Spring 2012 -- Lecture 3

  5. First law of thermodynamics System of study Q W Controlling medium PHY 341/641 Spring 2012 -- Lecture 3

  6. Examples of heat and work performed by ideal gas PHY 341/641 Spring 2012 -- Lecture 3

  7. Various ideal gas processes (assuming N constant) PHY 341/641 Spring 2012 -- Lecture 3

  8. Some details of the adiabatic case: Q = 0 PHY 341/641 Spring 2012 -- Lecture 3

  9. Ideal gas expansions DT = 0 DQ = 0 PHY 341/641 Spring 2012 -- Lecture 3

  10. Work performed during a cyclic process: PHY 341/641 Spring 2012 -- Lecture 3

  11. Efficiency of cyclic processes: The notions of work and heat can be used for practical devices Example: Internal combustion engine Otto cycle: http://www.howstuffworks.com/engine1.htm General measure of process efficiency (assuming no frictional losses; “completely reversible processes”): PHY 341/641 Spring 2012 -- Lecture 3

  12. PHY 341/641 Spring 2012 -- Lecture 3

  13. Analysis of an ideal heat engine Nicholas Carnot (French Engineer) 1834 isothermal adiabatic adiabatic isothermal PHY 341/641 Spring 2012 -- Lecture 3

  14. Analysis of Carnot cycle for ideal gas system PHY 341/641 Spring 2012 -- Lecture 3

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