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

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

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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).

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.

Thermal Expansion

- Heat makes molecules vibrate more, move apart.
- Materials expand, holes in material expand.

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.

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.

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