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AP Physics Chapter 15 The Laws of Thermodynamics

AP Physics Chapter 15 The Laws of Thermodynamics. Thermodynamics is the study of processes in which energy is transferred as heat and as work. A system is an object or set of objects to be considered. A closed system is where no mass enters or leaves a system.

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AP Physics Chapter 15 The Laws of Thermodynamics

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  1. AP Physics Chapter 15 The Laws of Thermodynamics Thermodynamics is the study of processes in which energy is transferred as heat and as work. A system is an object or set of objects to be considered. A closed system is where no mass enters or leaves a system. Open systems can lose or gain mass to the environment. An isolated system is a closed system where no energy crosses the system boundary.

  2. 15-1 The First Law of Thermodynamics • DU=Q – W • The first law of thermodynamics is a statement of the conservation of energy law. • See Example 15-1 p444

  3. 15-2 First Law of Thermodynmics Applied to Some Simple Systems • An isothermal process that is conducted with a constant temperature. • Isotherms are lines of equal temperature… see page 445. • A heat reservoir is a location of heat so large that it provides a isothermal environment. • Adiabatic processes allow no heat energy to flow into or out of the system.

  4. 15-2 (cont’d) • An isobaric process is one in which pressure is kept constant. • An Isochoric or isovolumetric process is one in which volume is held constant. • See Conceptual Examples 15-2 and 15-3 p447. • See Example 15-4, 15-5, and 15-6 p448.

  5. 15-3 Human metabolism…the 1st Law • Metabolism is the name given to the energy producing and using reactions in living things. • DU=Q – W • See Example 15-7

  6. The 2nd Law of Thermodynamics • …Heat flows from a hot object to a cold object; heat will not flow spontaneously from a cold object to a hot object. • A heat engine is any device that changes thermal energy into mechanical work.

  7. 15-5 Heat Engines • QH=W + QL …where QH is the heat input, W is work, and QL is heat exhausted… all positive in value. (See diagram p 451) • Temperature difference is required to run an engine. • Effieciency… • e=W/QH=(QH-QL)/QH= 1-(QL/QH) • See Example 15-8 p453

  8. 15-5 (cont’d) • Sadi Carnot (1796-1832) examined the ideal engine, now called a Carnot engine…the process of heat addition and exhaust were done reversibly, so that the process was considered a series of equilibrium states… real processes are actually irreversible. • eideal= (TH-TL)/TH= 1- (TL/TH) • See Example 15-9 p 454

  9. HOMEWORK… • P471 pr#1-3, 5-8, 14-16, 17-20 due next BOP

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