Thermal Physics
Lecture 1
Dr.-Ing. Erwin Sitompul
President University
http://zitompul.wordpress.com
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Thermal Physics
Textbook and Syllabus
Textbook:
“Fundamentals of Physics”, Halliday, Resnick, Walker, John Wiley &
Sons, 8th Extended, 2008.
Syllabus:
Chapter 18: First Law of Thermodynamics
Chapter 19: Kinetic Theory
Chapter 20: Second Law of Thermodynamics
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Thermal Physics
Grade Policy
Final Grade = 10% Homework + 20% Quizzes +
30% Midterm Exam + 40% Final Exam +
Extra Points
 Homeworks will be given in fairly regular basis. The average of
homework grades contributes 10% of final grade.
 Written homeworks are to be submitted on A4 papers, otherwise
they will not be graded.
 Homeworks must be submitted on time, one day before the next
lecture. Late submission will be penalized by point deduction of –
10·n, where n is the total number of lateness made.
 There will be 3 quizzes. Only the best 2 will be counted. The
average of quiz grades contributes 20% of final grade.
 The maximum lateness in coming to class is 25 minutes,
otherwise attendance will not be counted.
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Thermal Physics
Grade Policy
 Midterm and final exams follow the schedule released by AAB
(Academic Administration Bureau).
 Make up of quizzes must be requested within one week after the
schedule of the respective quiz.
 Make up for mid exam and final exam must be requested directly
to AAB.
Thermal Physics
Homework 2
Emelie Raturandang
0029202400058
21 March 2027
No.1. Answer: . . . . . . . .
● Heading of Written Homework Papers (Required)
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Thermal Physics
Grade Policy
 In order to maintain the integrity, the maximum score of a make
up quiz or exam, upon discretion, can be set to 90.
 Extra points will be given if you solve a problem in front of the
class. You will earn 1 or 2.
 Lecture slides can be copied during class session. It is also
available on internet. Please check the course homepage regularly.
http://zitompul.wordpress.com
 The use of internet for any purpose during class sessions is
strictly forbidden.
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Thermal Physics
Chapter 18
First Law of Thermodynamics
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Chapter 18
First Law of Thermodynamics
Thermodynamics and Engineering
 One of the principal branches of physics that is closely related to
Engineering is thermodynamics.
 Thermodynamics is the study of thermal energy and its
applications. The main concern is heat and temperature, and their
relation to energy and work.
 Some relations between thermodynamics and engineering are:
 Automobile engineers are concerned with the heating of a car
engine and the effect of temperature to engine efficiency.
 Building physics engineers are concerned with the temperature
control inside a building.
 Process engineers are concerned with the cooling or heating of
the material in the production lines.
 Medical engineers are concerned with how a patient’s
temperature might distinguish between a viral infection or a
cancerous growth.
 Electrical engineers are concerned on how to design appliances
and electronic devices which can work without overheating
problems.
 Electrical Engineering students are concerned on how to pass
the Thermal Physics class with good grade....
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Chapter 18
First Law of Thermodynamics
Temperature
 The starting point in discussion of
thermodynamics is the concept of temperature
and how it is measured.
 As one of the seven SI base quantities,
temperature is measured on the Kelvin scale.
The unit is called kelvins, with the notation K.
 The temperature of a body has no upper limit,
but it does have a lower limit, the absolute zero
temperature, 0 kelvins or 0 K.
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Erwin Sitompul
Thermal Physics 1/8
Chapter 18
First Law of Thermodynamics
The Zeroth Law of Thermodynamics
 The properties of many bodies change as we alter their
temperature.
 For example, as their temperature increases, the volume of a
liquid increases, the length of a metal rod increases, the electrical
resistance of a wire increases, the pressure exerted by a confined
gas increases.
 We can use any one of these properties as the basis of an
instrument that will help us pin down the concept of temperature.
 Assume that we have a thermoscope, an instrument with digital
display that will display increasing number if it is heated or
decreasing number if it is cooled.
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Chapter 18
First Law of Thermodynamics
The Zeroth Law of Thermodynamics
 We now put the thermoscope (body T) into
intimate contact with another body (body A).
 The entire system is confined within a thickwalled insulating box.
 We let body T and body A be in thermal
equilibrium, where the value indicated by the
thermoscope does not change anymore.
 Next, we put body T into intimate contact
with another body B. We let the two bodies
come to thermal equilibrium at the same
reading of the thermoscope.
 The question: If we put bodies A and B into
intimate contact, are they immediately in
thermal equilibrium with each other?
 Zeroth Law of Thermodynamics:
“If bodies A and B are each in themal
equilibrium with a third body T, then A and B
are in thermal equilibrium with each other.”
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Chapter 18
First Law of Thermodynamics
Measuring Temperature
 The Triple Point of Water
 To set up a temperature scale, we pick some
reproducible thermal phenomenon as a standard
fixed point and assign a certain Kelvin
temperature to its environment.
 For technical reasons, the triple point of water is
selected. At this condition, liquid water, solid ice,
and water vapor coexist, at a certain value of
pressure and temperature.
 By international convention, the triple point of
water has been assigned a value of 273.16 K.
T3  273.16 K
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?Isn’t it supposed to be 273.15 K?
Erwin Sitompul
Thermal Physics 1/11
Chapter 18
First Law of Thermodynamics
Measuring Temperature
 The Constant-Volume Gas Thermometer
 The standard thermometer is based on the
pressure of a gas in a fixed volume.
 As shown on the next figure, the thermometer
consists of a gas-filled bulb connected by a
tube to a mercury manometer.
 By raising and lowering reservoir R, the
mercury level in the left arm of the U-tube can
always be brought to the zero of the scale to
keep the gas volume constant.
 The temperature of any body in thermal
contact with the bulb is then defined to be:
T  Cp
C
p
: a constant
: the pressure exerted by the gas
p0
ρ
h
: the atmospheric pressure
: the density of mercury
: the difference between the
mercury levels
 The pressure p is given by:
p  p0   gh
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Thermal Physics 1/12
Chapter 18
First Law of Thermodynamics
Measuring Temperature
 If we now put the bulb in a liquid with triplepoint temperature, the temperature now being
measured is:
T3  Cp3
 After eliminating C, the temperature can be
given as:
 p
 p
T  T3    (273.16)  
 p3 
 p3 
 With this thermometer, different
gases in the bulb give slightly
different results.
 However, as we use smaller and
smaller amounts of gas
(decreasing p3), the reading
converge nicely to a single
temperature.
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Chapter 18
First Law of Thermodynamics
The Celsius and Fahrenheit Scales
 In the Celsius scale (formerly called the
centigrade scale), the temperatures are
measured in degrees, and the Celsius
degree has the same size as the kelvin.
 The zero of the Celsius scale is shifted to
a more convenient value than absolute
zero.
TC  T  273.15
 The Fahrenheit scale employs a smaller
degree than the Celsius scale and a
different zero of temperature.
9
TF  TC  32
5
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Chapter 18
First Law of Thermodynamics
Checkpoint
The figure here shows three linear temperature scales with the
freezing and boiling points of water indicated.
(a) Rank the degrees on these scales by size, greatest first.
(b) Rank the following temperatures, highest first: 50°X, 50°W, and
50°Y.
(a) All tie
(b) 50°X, 50°Y, 50°W
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Chapter 18
First Law of Thermodynamics
Problem
Suppose you come across old scientific notes that describe a
temperature scale called Z on which the boiling point of water is
65.0°Z and the freezing point is –14.0°Z. To what temperature on
the Fahrenheit scale would a temperature of T = –98.0°Z
correspond?
180


98.0Z   32 
(84.0)  F
79.0


 159.4F
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Chapter 18
First Law of Thermodynamics
Thermal Expansion
 When the temperature of an object is raised, the body usually
exhibit thermal expansion.
 With the added thermal energy, the atoms can move a bit farther
from one another than usual, against the spring-like interatomic
forces that hold every solid together.
 Such thermal expansion is a property of material. Some of which
can be put to common use. Thermometers and thermostats may
be based on the differences in expansion between the components
of a bimetal strip (see below).
 Familiar liquid-in glass thermometers are based on the fact that
liquids such as mercury and alcohol expands to a different
(greater) extend than their glass containers.
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Chapter 18
First Law of Thermodynamics
Thermal Expansion
 Linear Expansion
 In the temperature of a metal rod of length L is raised by an
amount ΔT, its length is found to increase by an amount:
L  L  T
α
: coefficient of linear expansion
[/°C or /K]
 The coefficient of linear expansion
α depends on the material. It also
varies with temperature. But, for
most practical purposes it can be
taken as constant for a certain
material.
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Chapter 18
First Law of Thermodynamics
Thermal Expansion
 Volume Expansion
 If all dimensions of a solid expand with temperature, the volume of
that solid must also expand.
 If the temperature of a solid or liquid whose volume is V is
increased by an amount ΔT, the increase in volume is found to be:
V  V  T
  3
β
: coefficient of volume expansion
[/°C or /K]
?Can you find the exact relation?
● The same steel ruler at
two different temperature
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Chapter 18
First Law of Thermodynamics
Checkpoint
The figure here shows four rectangular metal plates, with sides of L,
2L, or 3L. They are all made of the same material, and their
temperature is to be increased by the same amount.
Rank the plates according to the expected increase in
(a) their vertical heights and
(b) their areas,
greatest first.
(a) 2 and 3 tie, then 1, then 4
(b) 3, then 2, then 1 and 4 tie
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Chapter 18
First Law of Thermodynamics
Problem
On a hot day in Las Vegas, an oil trucker loaded 37000 l of diesel
fuel. It encountered cold weather on the way to Utah, where the
temperature was 23.0 K lower than in Las Vegas, and where it
delivered its entire load.
How many liters did it deliver? The coefficient of volume expansion
for diesel fuel is 9.50×10–4/°C, and the coefficient of linear
expansion for its steel truck tank is 11×10–6/°C.
V  V  T
 (37000)(9.50 104 )(23.0)
 808.45 l
Vdelivered  V  V
 37000  808.45
 36191.55 l
?Who paid for the “missing” diesel fuel?
! Although looked much, the missing fuel is
only 2.2 % of the original load.
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Chapter 18
First Law of Thermodynamics
Temperature and Heat
 The temperature of a cup of hot coffee, left sitting
on a table, will fall –rapidly at first but then more
slowly– until it reaches room temperature  The
room and the coffee are then in thermal
equilibrium.
 Generalizing the situation, we describe the coffee
as a system (with temperature TS) and the room
environment as another system (with
temperature TE) .
 Our observation is that if TS ≠ TE, then TS will
change (TE can also change some) until the two
temperatures are equal and thus thermal
equilibrium is reached.
 Such a change in temperature is because of a
transfer of energy between the system and the
system’s environment. The transferred energy is
called heat and is symbolized with Q.
 Heat is positive when energy is
absorbed by the system.
 Heat is negative when energy is
released or lost by the system.
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Chapter 18
First Law of Thermodynamics
Temperature and Heat
 Heat is the energy transferred between a system and its
environment because of a temperature difference that exists
between them.
 Besides, energy can also be transferred between a system and its
environment as work W via a force acting on a system.
 By old definition, heat was measured in terms of its ability to raise
the temperature of water.
 In SI system, the calorie (cal) was defined as the amount of heat
that would raise the temperature of 1 g of water from 14.5°C to
15.5°C.
 In the British system, the British thermal unit (Btu) was defined
as the amount of heat that would raise the temperature of 1 lb of
water from 63°F to 64°F.
● 1 cal = 4.1868 Joule
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Chapter 18
First Law of Thermodynamics
Class Group Assignments
1.Unsatisfied with the Celsius and Fahrenheit temperature scales,
you decide to create your own. On your temperature scale, the ice
point is 77M and the steam point is at 437M, where “M” stands
for “my scale.” What temperature on your scale corresponds to
68F?
(a) 154 °M
(d) 168 °M
(b) 140 °M
(e) 136 °M
(c) 149 °M
2.A constant-volume gas thermometer is used to measure the
temperature of an object. When the thermometer is in contact with
water at its triple point (273.16 K), the pressure in the
thermometer is 8.950×104 Pa. When it is in contact with the
object, the pressure is 7.650×104 Pa. The temperature of the
object is:
(a) 23 K
(b) 233 K
(c) 310 K
(d) 314 K
(e) 2636 K
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Chapter 18
First Law of Thermodynamics
Class Group Assignments
3.A glass tube with the volume 200 cm3 is completely filled with
mercury at 20°C. If the temperature of the system is increased to
100°C, determine the amount of mercury that overflows. The
coefficient of linear expansion of glass is 0.34×10–5 K–1 while
coefficient of volume expansion of mercury is 1.82×10–4 K–1.
(a) 1.43 cm3
(d) 2.72 cm3
(b) 2.75 cm3
(e) 3.57 cm3
(c) 4.81 cm3
4.A brass cube, 10 cm on a side, is raised in temperature by 200°C.
The coefficient of volume expansion of brass is 57 × 10–6/°C. By
what percentage is any one of the 10-cm edges increased in
length?
(a) 4%
(d) 1.14%
(b) 0.38%
(e) 0.29%
(c) 0.17%
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Chapter 18
First Law of Thermodynamics
Class Group Assignments
5.A gram of distilled water at 4°C:
(a) will increase slightly in weight when heated to 6°C.
(b) will decrease slightly in weight when heated to 6°C.
(c) will increase slightly in volume when heated to 6°C.
(d) will decrease slightly in volume when heated to 6°C.
(e) will not change in either volume or weight.
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Chapter 18
First Law of Thermodynamics
Homework 1
1.(18-7) Suppose that on a linear temperature scale X, water boils
at –53.5°X and freezes at –170°X. What is a temperature of 340 K
on the X scale? (Approximate water’s boiling point as 373 K.)
2.(18-17) A steel rod is 3.000 cm in diameter at 25.00°C. A brass
ring has an interior diameter of 2.992 cm at 25.00°C. At what
common temperature will the ring just slide onto the rod? (Hint:
For coefficients, use only the value given by the textbook.)
 Deadline: 16 April 2015.
● Be sure to understand the homework problems.
● Validation tests will be conducted occasionally.
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