AP Physics B Summer Course 2012
2012年 AP物理 B暑假班
M Sittig
Ch 18: Thermodynamics
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