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Unformatted text preview: Physics II: Heat & Electromagnetism today: pV paths wrap-up (see last lectures notes) Heat Engines & Refrigerators Carnot cycle 2 nd law of thermodynamics Physics 213 Sept. 12, 2006 6.1 Engines, Refrigerators, Heat pumps 1st Law of Thermo: 0 = ! U = Q - W Engine: W cycle = Q H- |Q C | efficiency: Refrigerator: Q C = |Q H | - W cycle Coefficient of Performance (COP): Heat pump: |Q H | = Q C + W cycle Physics 213 Sept. 12, 2006 6.2 Engine U = 0 cycle W cycle Q H Q C | | Q C Q H | | U = 0 cycle W cycle T H T H T C T C Hot Thermal Reservoir Cold Thermal Reservoir Refrigerator/Heat pump Maximum efFciency? Irreversible process: Shufing an ordered set of cards Heat ow between objects in thermal contact but not in thermal equilibrium ( T H > T C ) riction Diffusion Reversible processes are processes where there is thermodynamic equilibrium , e.g.: Heat transfer between objects of (nearly) the same temperature ( T H ~ T C ) Phase changes with phases in...
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