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AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班 PowerPoint PPT Presentation


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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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Ch 18: Thermodynamics

AP Physics B Summer Course 20122012年AP物理B暑假班

M Sittig


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).


Example Problem


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.


Example Problem


Thermal Expansion

  • Heat makes molecules vibrate more, move apart.

  • Materials expand, holes in material expand.


Thermal Expansion


Example Problem


Ideal Gas Law

  • Just remember from Chemistry:

  • PV = nRT

  • Where n is moles.

  • Also in the form:

  • PV = NkBT

  • Where N is molecules.


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.


Example Problem


Example Problem


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 _____.


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.


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.


PV Diagrams


Heat Engines and Second Law of Thermodynamics


Entropy


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