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Physics 209
Fall 2013
Thermal Physics Class #14
Thermal Averages and the Equipartition Theorem
Friday, October 4, 2013
I. Thermal Averages
A. Expectation Value: The expectation value of a quantity A is given by
X
hAi =
(Probability of A) A.
poss. values o
Example Problem 1. The emissivity of tungsten is 0.35. A tungsten sphere with radius 1.50 cm is
suspended Within a large evacuated enclosure Whose walls are at 290 K. Find the electrical power input that
is required to maintain the sphere at temperature o
Example Problem 1. Example Heat Engine.
When thinking about heat engines, it is often useful to have a specic example in mind. Below is a silly,
but simple example of a heat engine which operates in a cycle that is used to lift sand to a platform. The
ass
Example Problem 1. A 1.0 kg ice block at 0C slowly melts in a room that is very slightly warmer than
the ice cube. Find the change in entropy of the ice cube.
A. Model. Is the process reversible? If not, what reversible process will you use to calculate t
Example Problem 1. You are asked to design the most efcient possible heat engine that can lift a 15 kg
mass 2.0 In each cycle While using 500 J of heat input from a high temperature reservoir that is at 500C. (a)
What type of cycle will you use? Sketch th
Entropy Changes in Macroscopic
Processes
Thermal Physics Class 16, Monday, October 1, 2012
NO Journal Club Monday
Chris Ramsey
Washington University Dual Degree Program
Tuesday, October 8th
12:10 p.m., Goodrich 104
Entropy of Ideal Monatomic Gas
By calcul
Phys 209 Homework #17
Due: Fri, Oct. 11
Name:
Problem 1. (20 points) A heat engine takes 0.350 moles of air around a cycle as follows:
1 2: The air initially at 300 K and 1.00 atm is heated isochorically until the temperature
doubles to 600 K.
2 3: Then t
Example Problem 1. Estimate the rms speed of an air molecule in a room at normal room temperature.
A. Model.
B. Visualize/Parameterize.
C. Math. [Formula First]
ID. Assess.
Solution.
A A$UVK +l 'lk/ \ptatl gas Racy/l 3x5 val)l
ma M, New ,2; Maj In, 6:490t
Physics 209
Spring 2013
Thermal Physics Class #3
Heat Conduction
Friday, September 6, 2013
I. Heat Conduction: Heat flow via direct thermal contact between bodies at different temperatures.
The rate of heat flow through a material of cross-sectional area
#WD!
goloJmom W
Name:
Problem 1. (10 points) Some 3.0 X 1022 molecules of nitrogen gas at 280 K are in a chamber with a piston
that expands isothermally to 3 times its original volume. (a) Sketch a PVdiagram of this process. (b)
Explain Why heat must en
HW 12 -
Name:
Problem 1. Consider two Einstein solids A (contains 1 atom) and B (contains 2 atoms) which have a
combined energy U A + U13 = 65. These systems, which are isolated from their surroundings, are placed
into thermal contact. (a) Without using
golUlYOY) 3 _HL
Problem 1. (10 points) Imagine that a quantum system has exactly three energy states, with energies 0.020
eV, 0.040 eV, and 0.060 eV, respectively. At room temperature, out of every 1000 of these systems, about
how many are in each state?
Name:
Phys 209 TP-HW#05
Due: Wed., Sep. 11
Problem 1. (10 points) The rate at which radiant energy from the sun reaches the earths upper atmosphere
is about 1370 W/m2 . The distance from the earth to the sun is 1.50 1011 m, and the radius of the sun is
6.
Physics 209
Spring 2013
Thermal Physics Class #0
Thermal Energy
Friday, August 30, 2013
I. Definitions
A. Heat (Q): The energy that flows across the boundary between two objects as a result of a
difference in temperature between them.
B. Work (W ): The en
TPHW16
g 0 ii) l )O M S =
Problem 1. (10 points) (a) Imagine that the temperature of a 220g block of aluminum sitting in the sun
increases from 18C to 26C. By how much has its entropy increased? (b) A puddle containing 0.80 kg of
water at 0C freezes on a
Physics 209
Fall 2013
Thermal Physics Class #8
Thermodynamic Processes
Wednesday, September 18, 2013
I. Thermodynamic Processes
A. Quasistatic Process: A process that occurs at rate much slower than the typical relaxation
times of the system so that it al
E ale 7* low c; W
Name:
Problem 1. (10 points) Your lab partner claims that physicists have it all backward: cold things actually
have more thermal energy than hot things, and energy actually ows from cold to hot. What evidence could 1
you point out that
HW08
90 mm -
Problem 1. (10 points) Argon gas is conned to a cylinder With a piston. The gas has an initial pressure
of 120 kPa and a volume of 100 cm3. The piston is slowly Withdrawn until the gass volume has increased by
0.5%. (a) Estimate the work done
TPHWl 5 I
Name:
Problem 1. (10 points) Consider a molecule that has 4 energy levels, 1 level with energy E1, 1 level with
energy 2E1, and 2 levels which have energy 3E1. (a) If each level is equally likely, nd the average energy
(E) of this molecule. (