8 Zeroth Law of Thermodynamics
The Zeroth Law of Thermodynamics states that if two systems are in ther-
modynamic equilibrium with a third system, the two original systems are in
thermal equilibrium with each other.
Figure 2: Zeroth Law of Thermodynamics: The double arrow represents
thermal equilibrium between systems. If systems A and C are in equilib-
rium, and systems A and B are in equilibrium, then systems B and C are in
equilibrium. The systems A, B, and C are at the same temperature.
9 Measurement of Temperature
Temperature is a measure of the average kinetic energy of the particles in
matter. In everyday usage, temperature indicates a measure of how hot or
cold an object is.
Zeroth law of thermodynamics is the basis of temperature measurement.
In order to obtain a quantitative measure of temperature, a reference body
is used, and a certain physical characteristic of this body which changes with
temperature is selected. The change in the selected characteristic may be
taken as an indication of change in temperature. The selected characteristic
is called the thermometric property, and the reference body which is used
in the determination of temperature is called the thermometer. A very
common thermometer consists of a small amount of mercury in an evacuated
capillary tube. In this case, the extension of the mercury in the tube is used
as the thermometric property.
9.1 reference Points
Temperature scales enable us to use a common basis for temperature mea-
surements. All temperature scales are based on some easily reproducible
states such as the freezing and boiling points of water, which are also called
the ice point and the steam point, respectively. A mixture of ice and water
that is in equilibrium with air saturated with vapor at 1 atm pressure is said
9
The Zeroth Law of Thermodynamics states that if two systems are in ther-
modynamic equilibrium with a third system, the two original systems are in
thermal equilibrium with each other.
Figure 2: Zeroth Law of Thermodynamics: The double arrow represents
thermal equilibrium between systems. If systems A and C are in equilib-
rium, and systems A and B are in equilibrium, then systems B and C are in
equilibrium. The systems A, B, and C are at the same temperature.
9 Measurement of Temperature
Temperature is a measure of the average kinetic energy of the particles in
matter. In everyday usage, temperature indicates a measure of how hot or
cold an object is.
Zeroth law of thermodynamics is the basis of temperature measurement.
In order to obtain a quantitative measure of temperature, a reference body
is used, and a certain physical characteristic of this body which changes with
temperature is selected. The change in the selected characteristic may be
taken as an indication of change in temperature. The selected characteristic
is called the thermometric property, and the reference body which is used
in the determination of temperature is called the thermometer. A very
common thermometer consists of a small amount of mercury in an evacuated
capillary tube. In this case, the extension of the mercury in the tube is used
as the thermometric property.
9.1 reference Points
Temperature scales enable us to use a common basis for temperature mea-
surements. All temperature scales are based on some easily reproducible
states such as the freezing and boiling points of water, which are also called
the ice point and the steam point, respectively. A mixture of ice and water
that is in equilibrium with air saturated with vapor at 1 atm pressure is said
9
