chapter 7 temperature and zeroth law new
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Fundamental Physics
Chapter 7
PETROVIETNAM UNIVERSITY
FACULTY OF FUNDAMENTAL SCENCES
Hanoi, August 2012
Pham Hong QuangE-mail: quangph@pvu.edu.vn
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Chapter 7 Temperature, Heat, and the Frst Lawof Thermodynamics
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7.1 Temperature and Zeroth law of
Thermodynamics
7.2 Thermal Expansion
7. The !irst "aw of Thermodynamics
7.# Thermodynamic Processes
7.$ Heat Transfer
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7.1 Temperature and Zeroth law of Thermodynamics
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The standard scale of temperature is Kelvin.
The Kelvin scale is setup so that its zero point is
the coldest possible temperature--absolute zero,
at which point a substance would have zero
internal energy. Absolute zero can never be
reached, but there is no limit to how close we can
get to it. Scientists have cooled substances to
within 1-!
Kelvins of absolute zero. "ow do we#now how cold absolute zero is, if nothing has
ever been at that temperature$ The answer is by
graphing %ressure vs. Temperature for a variety of
gases and e&trapolating.
Temperature measures the %speed& of the
molecules
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7.1 Temperature and Zeroth law of Thermodynamics
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The zeroth law of thermodynamics:
•If two systems are each in thermal
equilibrium with a third, then they are in
thermal equilibrium with one another.
•'f two thermal systems are in thermal e(uilibrium
with one another, then they have the same
temperature.
• Temperature is the indicator of thermal e(uilibrium
in the sense that there is no net )ow of heat
between two systems in thermal contact that have
f
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7.1 Temperature and Zeroth law of Thermodynamics
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't wor#s based on thevariation of pressure of a*&ed volume gas as its
temperature changes. The volume of the gas is#ept constant by raising orlowering the reservoir + to
#eep the mercury level at Aconstant. The pressure is indicatedby the height dierencebetween reservoir + and
column A.
'onstant ()olume
*as Thermometer
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7.1 Temperature and Zeroth law of Thermodynamics
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To *nd the temperature of a substance, the gas)as# is placed in thermal contact with thesubstance.
The thermometer readings are virtuallyindependent of the gas used.'f the lines for various gases are e&tended, thepressure is always zero when the temperature is
/0.1!o
. This temperature is called a+solute ,ero.Absolute zero is used as the basis of thea+solute temperature scale.
'onstant()olume *as Thermometer-
'ont.
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7.1 Temperature and Zeroth law of Thermodynamics
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Thermodynamics
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How do you cali+rate yourthermometer
•+y international agreement the triple point of water
has been assigned the value of /0.12 K.
•elsius scale3 't means3 Tc at
the triple point is .1 elsius degree.
•4ahrenheit scale
T
F =
9
5T C + 32 = 32.02oF
=
→ 30lim16.273
p p K T
m
15.273−=T T c
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Thermodynamics
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Thermodynamics
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Temperature Measurement -Some Thermometers
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7.2 Thermal Expansion
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The volume of matter
e&pands when the atomic
spacing increases.
'ncrease temperature
5 increase volume.
T V V ∆=∆ 0β
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7.2 Thermal Expansion
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•4or small volumechanges therelationship betweenvolume and
temperature is linear.
• The coe6cient ofvolume e&pansion isβ.
7aterial oe6cient β8uartz 1 & 1-2 °-1
%yre& glass 9 & 1-2 °-1
:lass / & 1-2 °-1
Steel 0! & 1-2 °-1
Aluminum /! & 1-2 °-1
7ercury 1; & 1-2 °-1
1 atm? 0@ & 1-2 °-1
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7.2 Thermal Expansion
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•7ost substancese&pand uniformlywith temperature.
•
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7.2 Thermal Expansion
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The change involume applies tothe threedimensions.
'f the change ise(ual in alldirections β is splitin thirds.
The coe6cient oflinear e&pansion insolids >α? is usually
one third of β.
W H L HW LW LH V
W H LV
∆+∆+∆≅∆
=
000000
0000
)3
(
)3
(
)3
(
000
000
000
W T H L
W H T L
W H LT V
β
β
β
∆+
∆+
∆≅∆
3/
0
β α
α
=∆=∆ LT L
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7.2 Thermal Expansion
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7.3 The First Law of Thermodynamics
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Thermodynamics is the study of the inter-relation between heat, wor# and internalenergy of a system and its interaction with itsenvironment..
Thermodynamics
=&le systems• :as in a container• 7agnetization and
demagnetization•
harging Bdischarging a battery
• hemical reactions• Thermocouple
operation
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7.3 The First Law of Thermodynamics
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Thermodynamics tates
A state /aria+le describes the stateof a system at time t, but it does notreveal how the system was put into
that state.=&les of state variables3• % C pressure >%a or DEm?,• T C temperature >K?,•
C volume >m0
?,• n C number of moles, and• F C internal energy >G?.
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7.3 The First Law of Thermodynamics
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0hat is heat
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7.3 The First Law of Thermodynamics
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Specific Heats c at Room
Temperature
Substance Joules/kg/K
lead 128
copper 386
aluminum 900
glass 840
water 4190
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7.3 The First Law of Thermodynamics
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Heats of Transformation
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7.3 The First Law of Thermodynamics
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To vaporize a li(uid means to change it fromthe li(uid state to the vapor or gas state.
This process re(uires energy because themolecules must be freed from the li(uid state.ondensing a gas to a li(uid is the reverse of
vaporizing it re(uires that energy be removedfrom the gas so that the molecules can clustertogether instead of )ying away from eachother.
The heat of transformation for these phase
changes is called the heat of /apori,ation,Jv. vLmQ ⋅=
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7.3 The First Law of Thermodynamics
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The internal energy of a system changesfrom an initial value Ui to a nal value of
Uf due to heat Q and work W.
Q is positive when the system gains heat andnegative when it loses heat. W is positive
when wor# is done by the system andnegative when wor# is done on the system.
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7.3 The First Law of Thermodynamics
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!am"le $.
Positi/e and 4egati/e0or5
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7.4 Thermodynamic Processes
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A thermodynamic process is represented by a
change in one or more of the thermodynamicvariables describing the system.
=ach point on the curverepresents ane(uilibrium state of thesystem.
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7.4 Thermodynamic Processes
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The area under apressure-volume graph isthe wor# for any #ind of
process. The colored area givesthe wor# done by the gasfor the process from X to
Y .
!"r# and the Area Under a Pressure$
%"lume &raph
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7.4 Thermodynamic Processes
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Chec# Y"ur Understandin'
74Thermodynam cProcesses
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7.4 Thermodynam c Processes
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6n iso+aric process
is one that occurs at constant pressure.
4or an isobaricprocess, a pressure-versus-volume plot isa horizontal straight
line, and the wor#done LW C P>V f
V i?M is the colored
rectangular area
under the graph.
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7.4 Thermodynamic Processes
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The substance in thechamber is
e&pandingisobarically becausethe pressure is heldconstant by the
e&ternal atmosphereand the weight ofthe piston and thebloc#.
6n iso+aric process-
cont.
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7.4 Thermodynamic Processes
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Example 3.
s"(aric E)pansi"n "* !ater
Nne gram of water is placed in the cylinder in above
*gure, and the pressure is maintained at . O 1!
%a. The temperature of the water is raised by 01 P.'n one case, the water is in the li(uid phase and
e&pands by the small amount of 1. O 1; m0. 'n
another case, the water is in the gas phase and
e&pands by the much greater amount of /.1 O 1!
m0. 4or the water in each case, *nd >a? the wor#
done and >b? the change in the internal energy.
c # $%&' (!g*+)
c P # -- (!g*+).
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7.4 Thermodynamic Processes
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>a?
>b?
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7.4 Thermodynamic Processes
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sochoric process 8'sometric?
one that occurs at constant volume.
>a?The substance in the chamberis being heated isochoricallybecause the rigid chamber#eeps the volume constant.
>b?The pressure-volume plot foran isochoric process is avertical straight line. The area
under the graph is zero,indicating that no wor# isdone. 't means that thechange in the internal energye(uals the heat transfer3
QF C 8
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7.4 Thermodynamic Processes
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There is adia+atic process, one that occurs
without the transfer of heat . Since there is no
heat transfer, Q e(uals zero, and the *rst law
indicates that C Q W C W . Thus,
when wor# is done by a system adiabatically,
W is positive and the internal energy of the
system decreases by e&actly the amount of
the wor# done.
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7.4 Thermodynamic Processes
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6dia+atic process-
cont.
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7.4 Thermodynamic Processes
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isothermal process,one that ta#es place at
constant temperature. 'n
an isothermal process,
both % and of the gas
change
sothermal process
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7.4 Thermodynamic Processes
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=== ∫ ∫
i
f
v
v
v
v v
vnRT
V
nRTdV PdV W
f
i
f
i
ln
Thermal Pr"cesses Usin' an deal &as+ E)ample
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7.4 Thermodynamic Processes
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Two moles of the monatomic gas argon e&pandisothermally at 9; K, from an initial volume of V i
C .! m0 to a *nal volume of f C .! m0.
Assuming that argon is an ideal gas, *nd >a? thewor# done by the gas, >b? the change in theinternal energy of the gas, and >c? the heatsupplied to the gas.
Thermal Pr"cesses Usin' an deal &as
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75HeatTransferMechanism
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7.5 Heat Transfer Mechanism
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Conduction
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7.5 Heat Transfer
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Substance k (W/m . K)
Stainless steel 14
Aluminum 235
Copper 401
Polyurethane foam 0.024
Air 0.026
'onduction>Through solid slabs?
Q
t = kA(T
H − T
C )
L
%cond
C 8 E t
>energyEtime?
75HeatTransfer
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7.5 Heat Transfer
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9ate through each sla+ are e:ual in
steady state
Pcond = k 1 A(T x − T C )
L1= k 2 A(T H − T x )
L2
Pcond = A(T H −T C )
L1
k 1+ L2
k 2
Pcond = A(T H − T C ) L1k 1
+ L2
k 2+ L3
k 3
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7.5 Heat Transfer
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'on/ection
'on/ection and ;uoyancy
- onvection occurs because when a )uid such
as air or water is heated its density
decreases.
- 't rises up through a buoyant force .
- The heated air from a candle )ame or hot
stove rises because of this.
- Ue(uires a medium
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7.5 Heat Transfer
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75HeatTransfer
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7.5 Heat Transfer
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75HeatTransfer
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7.5 Heat Transfer
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75HeatTransfer
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7.5 Heat Transfer
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Emission experimenteperiment
75HeatTransfer
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7.5 Heat Transfer
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Absorption experiment
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Thank you%
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