1. Chapter 21
Temperature

2. Without external forces
System K, U

3. Work done on a system by external forces
Thermal Physics
System K, U
Mechanical Energy

4. Thermal Physics
Mechanical Physics ?

5. Macroscopic
Thermal Physics
Microscopic

6. Concept of Temperature
System of Temperature
Measuring of Temperature

7. Temperature systems:
— Kelvin temperature
— Celsius temperature
— Fahrenheit temperature

8. — Kelvin temperature
Absolute zero as zero
Ice
Water
Vapor
Triple-point
Triple-point as K

9. — Fahrenheit temperature
— Celsius temperature
Tc=T
— Fahrenheit temperature
TF=(9/5)Tc+32

10. Some interesting facts
T (K)
108
107
106
105
104
103
100 10 1
0.1
Hydrogen bomb
In 1724, Gabriel Fahrenheit made thermometers using mercury. The zero point of his scale is attained by mixing equal parts of water, ice, and salt. A second point was obtained when pure water froze (originally set at 30oF), and a third (set at 96oF) “when placing the thermometer in the mouth of a healthy man”.
On that scale, water boiled at 212.
Later, Fahrenheit moved the freezing point of water to 32 (so that the scale had 180 increments).
In 1745, Carolus Linnaeus of Upsula, Sweden, described a scale in which the freezing point of water was zero, and the boiling point 100, making it a centigrade (one hundred steps) scale. Anders Celsius ( ) used the reverse scale in which 100 represented the freezing point and zero the boiling point of water, still, of course, with 100 degrees between the two defining points.
Sun’s interior
Solar corona
Sun’s surface
Copper melts
Water freezes
Liquid nitrogen
Liquid hydrogen
Liquid helium
Lowest T
~ 10-9K

11. Boiling of Water Freezing of Water Boiling of LN Absolute zero
Kelvin
Celsius
Freezing of Water
Boiling of LN
Absolute zero
Fahrenheit
TF=(9/5)Tc+32

12. Measuring temperature with physical quantity proportional to T:
thermoresistance R G

13. Measuring temperature with physical quantity proportional to T:
thermocouple V
NiAl
NiCrAl

14. Measuring temperature with physical quantity proportional to T:
Constant Volume Gas Thermometer:
Constant Pressure Solid Thermometer:

15. Absolute Zero
The thermometer readings are virtually independent of the gas used
If the lines for various gases are extended, the pressure is always zero when the temperature is –273.15o C
This temperature is called
absolute zero
Absolute zero is used as the basis of the absolute temperature scale
The size of the degree on the absolute scale is the same as the size of the degree on the Celsius scale
To convert: TC = T –

16. Constant Volume Gas Thermometer:

17. The zeroth law of thermaldynamic
Thermal Equilibrium
Thermal Contact:
Thermal insulating
Thermal Conducting TA A TB B T A B TA A TB B Q
TA=T TB =T
TA< TB
The zeroth law of thermaldynamic

18. Thermal expansion amount of expansion depends on…
change in temperature
original length
coefficient of thermal expansion

19. Thermal expansion

20. Temp: T L0

21. L =  L0 T (linear expansion)
Temp: T L0
Temp: T+T L
L =  L0 T (linear expansion)
A = g A0 T (area expansion)
V =  V0 T (volume expansion)

22. A = g A0 T (area expansion)
L=L0+L =L0 + a L0 T
L2=(L0+L) 2 =(L0 + a L0 T) 2
=L a L0 2 T+(a L0 T) 2
=L a L0 2 T
A=A0+A =A0 + g A0 T
g =2a
V =  V0 T (Volume expansion)
L 3 =L a L0 3 T
b =3a

23. Microscopic of Thermal Expansion
When temperature rises
molecules have more kinetic energy
they are moving faster, on the average
consequently, things tend to expand

25. L =  L0 T (linear expansion)
Temp: T L0
Temp: T+T L
L =  L0 T (linear expansion)
a = a (T)

26. Thermal Expansion
T = 0 C
T = 100 C
Most objects DO expansion with T

27. Thermal Expansion T = 0 C T = 100 C Most objects DO expansion with T
Water has a maximum density at 40C

28. Bimetallic Strip

29. Bimetallic Strip

30. Bimetallic Strip

31. 220V

32. 220V

33. The Ideal Gas The number of particles is “large”
All particles are in random motion
The volume of the particles is small
There is no interaction between them
The collision is perfectly elastic

34. V=const.
p=const.
T=const.

35. The Ideal Gas
The real Gas
The number of particles is “large”
All particles are in random motion
The volume of the particles is not small
The volume of the particles is small
There is interaction between them
There is no interaction between them
The collision is perfectly elastic

36. Problem: To
B = rTo V g
The mass of a hot-air balloon and its cargo (not including the air inside) is 200 kg. The air outside is at 10.0°C and 101 kPa. The volume of the balloon is 400 m3. To what temperature must the air in the balloon be heated before the balloon will lift off ?
(Air density at 10.0°C is 1.25 kg/m3.)
V, T
rTVg m mg
T = 472 K !

37. CHAP. 21 Problems
P , 4
P , 10, 11