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AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班

Ch 18: Thermodynamics. AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班. M Sittig. Heat, Temperature and Power. Thermal energy: ( E therm ) Internal energy: The sum of all energies of all molecules in a substance (U).

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AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班

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  1. Ch 18: Thermodynamics AP Physics B Summer Course 20122012年AP物理B暑假班 M Sittig

  2. Heat, Temperature and Power • Thermal energy: (Etherm) • Internal energy: The sum of all energies of all molecules in a substance (U). • Temperature: Related to the average kinetic energy per molecule in a substance (T). • Heat: Thermal energy (Q). • Power: Work per time, rate of use of energy (P).

  3. Example Problem

  4. Rate of Heat Transfer • H=k·A·ΔT/L (= Q/t) • Directly proportional to • Thermal conductivity (k) • Area • Temperature Difference. • Inversely proportional to • Length • Think of it like water flowing through a pipe.

  5. Example Problem

  6. Thermal Expansion • Heat makes molecules vibrate more, move apart. • Materials expand, holes in material expand.

  7. Thermal Expansion

  8. Example Problem

  9. Ideal Gas Law • Just remember from Chemistry: • PV = nRT • Where n is moles. • Also in the form: • PV = NkBT • Where N is molecules.

  10. Ideal Gas Law • Remember that the ideal gas law summarizes the three smaller gas laws: • Boyle’s Law: V ~ 1/P • Charle’s Law: V ~ T • Pressure Law: P ~ T • But you don’t have to memorize these, just remember the Ideal Gas Law.

  11. Example Problem

  12. Example Problem

  13. Kinetic Theory of Gases • Molecules move in continuous, ____ motion. • There are a _____ number of molecules in any container of gas. • The _____ between gas molecules is large. • Molecules do not act on one another at a ____. • All collisions between molecules, and of molecules on container walls, are _____.

  14. Kinetic Theory of Gases • U = (3/2) nRT: most important thing is that internal energy (U) is directly proportional to (T), and only T. • vrms = sqrt( 3kBT/m ): most important thing is that T is related to KE, so you need a square root and the mass of a molecule to find v.

  15. First Law of Thermodynamics • Comes from the conservation of energy, so think about what flows in and out. • ΔU = change in internal energy of a sample of gas. • It can be positive (U increasing) if: • Q = heat flows into the gas • W = work is done on the gas • If heat flows out or work is done by the gas, the value of Q or W is negative and U decreases.

  16. PV Diagrams

  17. Heat Engines and Second Law of Thermodynamics

  18. Entropy

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