about temperature,heat and thermodynamics

about heat and thermodynamics

1. Chapter 16. Temperature Chapter 16. Temperature
and Expansionand Expansion
A PowerPoint Presentation byA PowerPoint Presentation by
Paul E. Tippens, Professor of PhysicsPaul E. Tippens, Professor of Physics
Southern Polytechnic State Southern Polytechnic State
UniversityUniversity
© 2007

2. TEMPERATURE is a measure of the average kinetic TEMPERATURE is a measure of the average kinetic
energy per molecule. The infrared radiation coming energy per molecule. The infrared radiation coming
from the air canal in the ear passes through the optical from the air canal in the ear passes through the optical
system of the thermometer and is converted to an system of the thermometer and is converted to an
electrical signal that gives a digital reading of body electrical signal that gives a digital reading of body
temperature. temperature.
Photo by
Blake Tippens

3. Objectives: After finishing Objectives: After finishing
this unit, you should be able this unit, you should be able
to:to:
•Work with Celsius, Kelvin, and
Fahrenheit temperature scales for
both specific temperatures and
temperature intervals.
•Write and apply
formulas for linear,
area, and volume
expansion.

4. Thermal EnergyThermal Energy
Thermal energyThermal energy is the total internal energy of an object: is the total internal energy of an object:
the sum of its molecular kinetic and potential energies.the sum of its molecular kinetic and potential energies.
Thermal energy = U + K
U = ½kx
2
K = ½mv
2
Internal energy -- spring analogies are helpful:

5. TemperatureTemperature
Temperature is related to the kinetic activity
of the molecules, whereas expansion and
phase changes of substances are more
related to potential energy.
2
½mv
T
N


Although not true in all cases, a good
beginning is to define temperature as the
average kinetic energy per molecule.

6. Temperature vs. Internal EnergyTemperature vs. Internal Energy
The large pitcher and
the small one have
the same temperature,
but they do not have
the same thermal
energy. A larger
quantity of hot water
melts more of the ice.

7. Temperature EquilibriumTemperature Equilibrium
Heat is defined as the
transfer of thermal energy
that is due to a difference
in temperature.
Hot Coals
Cool WaterSame Temperature
Thermal Equilibrium
Insulated
Container
Two objects are in
thermal equilibrium if
and only if they have the
same temperature.

8. ThermometerThermometer
A thermometer is any
device which, through
marked scales, can give an
indication of its own
temperature.
T = kX
X is thermometric property: Expansion, electric
resistance, light wavelength, etc.

9. Zeroth Law of Zeroth Law of
ThermodynamicsThermodynamics
The Zeroth Law of Thermodynamics:The Zeroth Law of Thermodynamics: If two objects If two objects AA and and
BB are are separatelyseparately in equilibrium with a third object in equilibrium with a third object CC, then , then
objects objects A A and and BB are in thermal equilibrium with each are in thermal equilibrium with each
other.other.
A
Object C
A B
Thermal Equilibrium
Same Temperature
B
Object C

10. 100
0
C 212
0
F
0
0
C 32
0
F
Temperature ScalesTemperature Scales
The lower fixed point is the
ice point, the temperature at
which ice and water coexist
at 1 atm of pressure:
0
0
C or 32
0
F
The upper fixed point is the
steam point, the temperature
at which steam and water
coexist at 1 atm of pressure:
100
0
C or 212
0
F

11. Comparison of Temperature Comparison of Temperature
IntervalsIntervals
212
0
F
32
0
F
180 F
0
100
0
C
0
0
C
100 C
0
t
C t
F
Temperature Intervals:
100 C
0
= 180 F
0
5 C
0
= 9 F
0
If the temperature
changes from 79
0
F to
70
0
F, it means a
decrease of 5 C
0
.

12. Temperature LabelsTemperature Labels
If an object has a specific temperature, we place the If an object has a specific temperature, we place the
degree symboldegree symbol
00
beforebefore the scalethe scale ((
00
CC or or
00
FF).).
t = 60t = 60
00
CC
We say: “The temperature is sixty
degrees Celsius.”

13. Temperature Labels (Cont.)Temperature Labels (Cont.)
If an object undergoes a If an object undergoes a change of temperaturechange of temperature, we , we
place the degree symbolplace the degree symbol
00
afterafter the scalethe scale ((CC
00
or or FF
00
) to ) to
indicate the interval of temperature.indicate the interval of temperature.
We say: “The temperature decreases by forty
Celsius degrees.”
t = 60
0
C – 20
0
C t = 40 C
0

tt
ii = 60 = 60
00
CC
tt
ff = 20 = 20
00
CC

14. Specific TemperaturesSpecific Temperatures
212
0
F
32
0
F
100
0
C
0
0
C
180 F
0
100 C
0
t
C t
F
Same temperatures
have different
numbers:
0
C
0
F
0 0
0 32
100 div 180 div
C F
t t 

09
5
32
C F
t t 
09
5
32
F Ct t   
05
9
32
C F
t t 

15. Example 1:Example 1: A plate of food cools from A plate of food cools from
160160
00
FF to to 6565
00
FF. What was the initial . What was the initial
temperature in degrees Celsius? What is temperature in degrees Celsius? What is
the change in temperature in Celsius the change in temperature in Celsius
degrees?degrees?
Convert 160
0
F to
0
C
from formula:
 
05
9
32
C F
t t 
0
0 05 5(128 )
(160 32 )
9 9
Ct   t
C
= 71.1
0
C
0 0 0
160 F 65 F 95 Ft    9 F
0
= 5 C
0
0
0
0
5 C
95 F
9 F
t
 
   
 
t = 52.8 C
0

16. Limitations of Relative Limitations of Relative
ScalesScales
The most serious problem with the Celsius
and Fahrenheit scales is the existence of
negative temperatures.
Clearly, the average kinetic
energy per molecule is NOT
zero at either 0
0
C or 0
0
F!
-25
0
C ?
T = kX = 0 ?

17. Constant Volume Constant Volume
ThermometerThermometer
Valve
Constant
volume of a
gas. (Air, for
example)
Absolute
pressure
A search for a true zero
of temperature can be
done with a constant-
volume thermometer.
For constant volume:
T = kP
The pressure varies with temperature.

18. Absolute Zero of Absolute Zero of
TemperatureTemperature
100
0
C0
0
C
P
1P
2
T
1
T
2
-273
0
C 0
0
C100
0
C
P
T
Plot points (P
1
, 0
0
C) and
(P
2
, 100
0
C); then
extrapolate to zero.
Absolute Zero = -273
0
C
Absolute
Zero

19. Comparison of Four Comparison of Four
ScalesScales
1 C
0
= 1 K
5 C
0
= 9 F
09
5
32
F Ct t 
 
05
9
32
C Ft t 
T
K = t
C + 273
0
ice
steam
Absolute
zero
100
0
C
0
0
C
-273
0
C
Celsius
C
Fahrenheit
32
0
F
-460
0
F
212
0
F
F
273 K
373 K
Kelvin
0

K
K
Rankine
0

R
460 R
672

R
R

20. Linear ExpansionLinear Expansion
L
L
o L
t
o
t
0
L L t  
0
L
L t




Copper:  = 1.7 x 10
-5
/C
0
Aluminum:  = 2.4 x 10
-5
/C
0
Iron:  = 1.2 x 10
-5
/C
0
Concrete:  = 0.9 x 10
-5
/C
0

21. Example 2:Example 2: A copper pipe is A copper pipe is 90 m90 m long at long at
2020
00
CC. What is its new length when steam . What is its new length when steam
passes through the pipe at passes through the pipe at 100100
00
CC??
L
o
= 90 m, t
0
= 20
0
C
t = 100
0
C - 20
0
C = 80 C
0
L = L
o
t = (1.7 x 10
-5
/C
0
)(90 m)(80 C
0
)
L
= 0.122 m L = L
o + L
L = 90 m + 0.122 m
L = 90.12 m

22. Applications of ExpansionApplications of Expansion
Expansion
Joints
Bimetallic Strip
Brass
Brass
Iron
Iron
Expansion joints are necessary to allow concrete to
expand, and bimetallic strips can be used for
thermostats or to open and close circuits.

23. Area ExpansionArea Expansion
Area expansion is analogous to
the enlargement of a photograph.
Example shows heated nut that shrinks
to a tight fit after cooling down.
Expansion on
heating.
A
0 A

24. Calculating Area ExpansionCalculating Area Expansion
W
L
L
L
o
W
o
W
A
0 = L
0W
0
A = LW
L = L
0 + L
0 t W
= W
0 + W
0 t
L = L
0(1 + t ) W
= W
0(1 + t
A = LW = L
0W
0(1 + t)
2
A = A
0(1 + 2t)
Area Expansion: A = 2

t

25. Volume ExpansionVolume Expansion
Expansion is the same
in all directions (L,
W, and H), thus:
V = V
0
t 
The constant  is the coefficient
of volume expansion. 0
V
V t





26. Example 3.Example 3. A A 200-cm200-cm
33
Pyrex beaker is Pyrex beaker is
filled to the top with glycerine. The filled to the top with glycerine. The
system is then heated from system is then heated from 2020
00
CC to to 8080
00
CC. .
How much glycerine overflows the How much glycerine overflows the
container?container?
V
ovr= ?
V
0 V
20
0
C
80
0
C
200 cm
3
Glycerine: 5.1 x 10
-4
/C
0
Pyrex:  =
3

0.3 x
10
-5
/C
0
)  = 0.9 x
10
-5
/C
0
V
over
= V
G
- V
P
V
ovr
= 
G
V
0
t - 
P
V
0
t = (
G
- 
P
)V
0
t
V
ovr = (5.1 x 10
-4
/C
0
- 0.9 x 10
-5
/C
0
)(200 cm
3
)(80
0
C - 20
0
C)

27. Example 3.Example 3. (CONTINUED) (CONTINUED)
V
ovr= ?
V
0 V
20
0
C
80
0
C
200 cm
3
Glycerine: 5.1 x 10
-4
/C
0
Pyrex:  =
3

0.3 x
10
-5
/C
0
)  = 0.9 x
10
-5
/C
0
V
over
= V
G
- V
P
V
ovr = 
GV
0 t - 
PV
0 t = (
G - 
P )V
0 t
V
ovr
= (5.1 x 10
-4
/C
0
- 0.9 x 10
-5
/C
0
)(200 cm
3
)(80
0
C - 20
0
C)
Volume Overflow = 6.01 cm
3

28. SummarySummary
Thermal energyThermal energy is the total internal energy of an object: is the total internal energy of an object:
the sum of its molecular kinetic and potential energies.the sum of its molecular kinetic and potential energies.
Thermal energy = U + K
The Zeroth Law of Thermodynamics:The Zeroth Law of Thermodynamics: If two objects If two objects AA and and
BB are are separatelyseparately in equilibrium with a third object in equilibrium with a third object CC, then , then
objects objects A A and and BB are in thermal equilibrium with each are in thermal equilibrium with each
other.other.
A B
Thermal EquilibriumA
Object C
B

29. Summary of Temperature Summary of Temperature
ScalesScales
1 C
0
= 1 K
5 C
0
= 9 F
09
5
32
F Ct t 
 
05
9
32
C Ft t 
T
K = t
C + 273
0
ice
steam
Absolute
zero
100
0
C
0
0
C
-273
0
C
Celsius
C
Fahrenheit
32
0
F
-460
0
F
212
0
F
F
273 K
373 K
Kelvin
0

K
K
Rankine
0

R
460 R
672

R
R

30. Summary: ExpansionSummary: Expansion
L
L
o L
t
o
t
0
L L t  
0
L
L t




Linear Expansion:
A = 2

t
Area Expansion:Expansion
A
0 A

31. Volume ExpansionVolume Expansion
Expansion is the same
in all directions (L,
W, and H), thus:
V = V
0
t 
The constant  is the coefficient
of volume expansion. 0
V
V t





32. CONCLUSION: Chapter 16CONCLUSION: Chapter 16
Temperature and ExpansionTemperature and Expansion