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8/10/2019 Phys2 Ch2 Heat Temp Law0
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PROGRAM OF PHYSICSLecturer:Dr. DO Xuan Hoi
Room 413
E-mail : [email protected]
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PHYSICS 2(FLUID MECHANICS AND THERMAL PHYSICS)
02 credits (30 periods)
Chapter 1 Fluid Mechanics
Chapter 2 Heat, Temperature and the Zeroth
Law of Thermodynamics
Chapter 3 Heat, Work and the First Law of
Thermodynamics
Chapter 4 The Kinetic Theory of Gases
Chapter 5 Entropy and the Second Law of
Thermodynamics
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References :
Halliday D., Resnick R. and Walker, J. (2005),Fundamentals of Physics, Extended seventh edition.John Willey and Sons, Inc.
Alonso M. and Finn E.J. (1992). Physics, Addison-WesleyPublishing Company
Hecht, E. (2000). Physics. Calculus, Second Edition.Brooks/Cole.
Faughn/Serway (2006), Serways College Physics,Brooks/Cole.
Roger Muncaster (1994), A-Level Physics, StanleyThornes.
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http://ocw.mit.edu/OcwWeb/Physics/index.htmhttp://www.opensourcephysics.org/index.html
http://hyperphysics.phy-
astr.gsu.edu/hbase/HFrame.htmlhttp://www.practicalphysics.org/go/Default.ht
ml
http://www.msm.cam.ac.uk/
http://www.iop.org/index.html...
http://www.opensourcephysics.org/index.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.htmlhttp://www.practicalphysics.org/go/Default.htmlhttp://www.practicalphysics.org/go/Default.htmlhttp://www.msm.cam.ac.uk/http://www.iop.org/index.htmlhttp://www.iop.org/index.htmlhttp://www.msm.cam.ac.uk/http://www.practicalphysics.org/go/Default.htmlhttp://www.practicalphysics.org/go/Default.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.htmlhttp://www.opensourcephysics.org/index.html8/10/2019 Phys2 Ch2 Heat Temp Law0
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CHAPTER 2
Heat, Temperature and the Zeroth
Law ofThermodynamics
Temperature and the ZerothLaw of
ThermodynamicsThermal Expansion (of Solids and Liquids)
Heat and the Absorption of Heat by Solidsand Liquids
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1. Temperature and the ZerothLaw of
Thermodynamics
What is HEAT ?
Heat is the transfer of energyfrom one object to another
object as a result of a difference in temperaturebetween
the two.Two objects are in thermal contactwith each other if
energy can be exchanged between them
Thermal equilibriumis a situation in which two objects inthermal contact with each other cease to exchange energy
by the process of heat.
These two objects have the same temperature
1.1 Notions
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Heat is the energy transferred between a
system and its environment because of atemperature difference that exists betweenthem.
Units: 1 cal = 4.1868 J
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A C
thermal
equilibrium
BC
thermal
equilibrium
AB?thermal
equilibrium
1.2 The zerothlaw of thermodynamics
(the law of equilibrium) : If objects A and B are separately in thermal equilibriumwith a third object C, then objects A and B are in thermalequilibrium with each other
thermometer
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If objects A and B are separately in thermalequilibrium with a third object C, then A andB are in thermal equilibrium with each other.
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1.3 Temperature Scales
Thermometers can be calibrated by placing them inthermal contact with an environment that remains atconstant temperature
Environment could be mixture of ice and water inthermal equilibrium
Also commonly used is water and steam in thermalequilibrium
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Comparing Temperature Scales
273.15
9325
9
5
C K
F C
F C
T T
T T
T T
=
= +
=
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TEST 1
What is the physical significance of the factor 9/5 in
Equation 9 325
F CT T= +
SOLUTION100 0 232 32 ;C C F F T T T T = 100 180C FT T=
180 91 ;100 5
C F FT T T= =
32 ;F FT T = 0C CT T =
915
C FT T=
1;
9 /5F C
F C
F
T TT T
T
=
5
9F CT T =
5( 32) 0 ;
9F CT T =
932
5F CT T= +
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PROBLEM 1
A healthy person has an oral temperature of 98.6 F. Whatwould this reading be on the Celcius scale?
SOLUTION
32 98.6 32 66.6F FT T F F F = = =
9
5 F CT T
66.6 166.6
9 /5
F CF
F
37.0 CC T= =
37.0 0C CT T=
37.0CT C=
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PROBLEM 2
A time and temperature sign on a bank indicates the outdoortemperature is -20.0C. Find the corresponding temperature onthe Fahrenheit scale.
SOLUTION9
1 5C FT T
20.0 9 /520.0
1
C FC
C
36.0 FF T= =
36.0 32FF T F =
4.0FT F=
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PROBLEM 3
On a day when the temperature reaches 50F, what is thetemperature in degrees Celsius and in kelvins?
SOLUTION
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PROBLEM 4
A pan of water is heated from 25C to 80C. What is thechange in its temperature on the Kelvin scale and on theFahrenheit scale?
SOLUTION
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2. Thermal expansion of solids
Thermalexpansion
Joints are used to
separate sections of
roadways on bridges
2.1 Notions
Thermal expansionis a consequence of thechange in the average separation betweenthe constituent atoms in an object
0
10A
0
11A
0
10A>
0
11A>
As the temperature of the solid increases, the atoms oscillate withgreater amplitudes the average separation between themincreases the object expands.
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2.2 Average coefficient of linear expansion
Li:initial length along some direction at some temperature Ti
L : amount of the increase in lengthT :change in temperature
The average coefficient of linear expansionis defined :
/ iL LT
= f i iL L L L T
The change in length of an object is proportional to thechange in temperature
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2.3 Average coefficient of volume expansion
Vi:initial volumeat some temperature
TiV : amount of the increase in volumeT :change in temperature
The average coefficient of volume expansionis defined :
/ iV VT
= f i iV V V V T
Relationship between and ?
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Consider a box of dimensions l, w, and h.Its volume at some temperature Ti is Vi= lwh
If the temperature changes to Ti+ T ,its volume changes to Vi+ V ,where each dimensionchanges according to :
( )( )( )iV V l l w w h h + = + + +
Relationship between and
i f iL L L L T =
( )( )( )l l T w w T h h T = + + + 3(1 )lwh T = + 2 31 3 3( ) ( )
iV T T T = + + +
Because for typical values of T < 100C, T
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The change in areaAi
of a rectangular platewhen the temperature change an amount of Tis
TEST
A. A = AiT
B.
A = 2
AiTC. A = 3AiT
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Principle of a thermostats:b im eta l l i c s t r ip
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A steel railroad track has a length of 30.000 m
when the temperature is 0.0C.
(a)What is its length when the temperature is 40.0C?
SOLUTION
The increase in length(a)
PROBLEM 5
iL L T = 6 111 10 ( ) (30000 )(40.0 )o oC m C =
The length of the track at 40.0C :
0.013 m=
0.013 30.013f iL L m m = + =
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A steel railroad track has a length of 30.000 mwhen the temperature is 0.0C.(a)What is its length when the temperature is 40.0C?
(b)Suppose that the ends of the rail are rigidly clampedat 0.0C so that expansion is prevented. What is the thermalstress set up in the rail if its temperature is raised to 40.0C?Knowing that the Youngs modulus for steel : 20 1010 N/m2.
SOLUTION (b)
PROBLEM 5
/
/ i
F AY
L L=
stress
Thermal stress : /i
LF A Y
L
=
10 7 20.013(20 10 / ) 8.7 10 /
30.000
F mN m N m
A m
= =
Youngs modulus:measuresthe resistance of a solid to a changein its length :
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A glass flask with volume 200 cm3is filled tothe brim with mercury at 20oC. How much mercury overflowswhen the temperature of the system is raised to 1OOC? The
coefficient of linear expansion of the glass is 0.40 1O-5
K-1
.SOLUTION
PROBLEM 6
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A metal rod is 40.125 cm long at 20.0oC and
40.148 cm long at 45.0C. Calculate the average coefficient of
linear expansion of the rod for this temperature range.
SOLUTION
PROBLEM 7
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A glass flask whose volume is 1000.00 cm3at0.0oC is completely filled with mercury at this temperature.When flask and mercury are warmed to 55.OoC, 8.95 cm3of
mercury overflow. If the coefficient of volume expansion ofmercury is 18.0 x 10-5K-1, compute the coefficient of volumeexpansion of the glass.
SOLUTION
PROBLEM 8
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3. Heat and the Absorption of Heat by Solidsand
Liquids
3.1 The specific heatThe heat capacity of a particular sample of asubstance is defined as the amount of energyneeded toraise the temperature of that sample by 1C.
If heat Q produces a change T in the temperature ofa substance :
Q C T=
J/0
CThe specific heat c of a substance is the heat capacityper unit mass
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If energy Q transferredby heat to mass m of asubstance changes thetemperature of the sample byT, then the specific heat ofthe substance:
Qc
m T
=
J/kg.0C
Q mc T =
N.B.: if c varies with temperature
over the interval (Ti , Tf) :f
i
T
T
Q m cdT =
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Consequences of Different Specific Heats
Water has a highspecific heat comparedto land
On a hot day, the airabove the land warmsfaster
The warmer air flows
upward and cooler airmoves toward thebeach
CkgJc
CkgJc
OH
Si
4186
700
2 =
=What happens at night?
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A 0.050 0-kg ingot of metal is heated to
200.0C and then dropped into a beaker containing 0.400 kg
of water initially at 20.0C.
(a)If the final equilibrium temperature of the mixed system is22.4C, find the specific heat of the metal.
SOLUTION
Conservation of energy : The energy leaving the hotpart of the system by heat is equal to that entering thecold part of the system
(a)
PROBLEM 9
cold hot Q Q=
The energy transfer for the water : ( ) ( 0)w w f w m c T T >The energy transfer for the sample of unknown specific heat :
( ) ( 0)x x f x m c T T