1. Temperature, Heat, and the Zeroth Law of Thermodynamics
Physics 213: Unit 2
Temperature, Heat, and the Zeroth Law of Thermodynamics

2. Thermodynamics Thermal Temperature
Thermodynamics deals with an internal energy of the systems, the thermal energy, and is governed by the Laws of Thermodynamics
Thermal Temperature

3. Zeroth Law of Thermodynamics
Temperature in daily life:
HOT
WARM
COOL
COLD
What is the definition of temperature ?
How to measure the temperature?
0th Law

4. 0th Law of Thermodynamics
If body A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other.
Thermal equilibrium: two objects in thermal contact cease to have any exchange of heat.
Thermal contact : Heat can be exchanged.
Heat: energy exchanged between objects due to their temperature difference.
Temperature : two objects in thermal equilibrium with each other are at the same temperature

5. Measuring Temperature
Bring a thermometer to a thermal equilibrium with the object
Thermometer: physical property changes with temperature
pressure of gas at constant volume
length of solid
Electric resistance
Volume of liquid

6. Temperature Scales DEFINE: Freezing temperature of water: 0˚C
Celsius scale
Boiling temperature of water: 100˚C
Constant-volume gas thermometer:
Measure Pressure Temperature
Different gases all extrapolate to zero pressure
at -273˚C: Kelvin scale

7. Temperature Scales Kelvin scale: T = 0 K for P = 0 point
Celsius scale: Tc = T ˚
Fahrenheit scale: TF = 9/5 Tc + 32˚
Thermodynamic scale: triple point of water
T3 = K

8. Thermal Expansion When heated, objects expand. Linear expansion:
Temperature
changes this much
Length changes
this much
Original
length
Coefficient of
linear expansion
Volume expansion:
Coefficient of
volume expansion

9. Unusual Behavior of Water
The maximum density occurs at 4 ˚C:
Above 4 ˚C, expands when heated
until 100 ˚C;
Below 4 ˚C, expands when cooled
until 0 ˚C.

10. Temperature and Heat
Internal energy: the energy of a system when it is stationary - nuclear, chemical, strain, etc.
Thermal energy: the energy that changes when the temperature changes, associated with motions of atoms, molecules, etc.
Heat Q: the transferred energy.

11. Units of Heat
Calorie: amount of heat to heat 1 g of water from 14.5 to 15.5 ˚C
BTU: amount of heat to heat 1 lb of water from 63 to 64 ˚F
SI: Joule (the same as energy)
1 cal = J
Joule’s experiment:

12. Constant-volume gas thermometer: P-T curve extrapolates to origin.
HRW 2E (5th ed.). Suppose the temperature of a gas at the boiling point of water is K. What then is the limiting value of the ratio of the pressure of the gas at that boiling point to its pressure at the triple point of water? (Assume the volume of the gas is the same at both temperatures.) P
T(K)
Constant-volume gas thermometer: P-T curve extrapolates to origin.

13. HRW 9E (5th ed.). At what temperature do the following pairs of scales read the same: (a) Fahrenheit and Celsius, (b) Fahrenheit and Kelvin, and (c) Celsius and Kelvin?
(c) Since
TC = T
the Kelvin and Celsius
temperatures can never have the
same numerical value.
(a) TF = (9/5)TC + 32˚
For TF = (9/5)TF + 32˚
we get TF = -40 ˚F
(b) TF = (9/5)TC + 32˚
= (9/5)(T ) + 32˚
For TF = (9/5) (TF ) + 32˚
we get TF = 575 ˚F

14. HRW 28P (5th ed. ). At 20˚C, a rod is exactly 20
HRW 28P (5th ed.). At 20˚C, a rod is exactly cm long on a steel ruler. Both the rod and the ruler are placed in an oven at 270˚C, where the rod now measures cm on the same ruler. What is the coefficient of thermal expansion for the material of which the rod is made of?
The change in length for the rod is 20.11cm-20.05cm plus
the expansion of the steel ruler at its 20.11cm mark:
∆Ls = Lsas∆T = (20.11 cm)(11 x 10-6 /C˚)(270˚C-20˚C)
= cm
∆L = (20.11cm-20.05cm) cm = cm
The coefficient of thermal expansion of the material the rod
is made of is:
a = ∆L/L∆T=23 x 10-6 /C˚