Temperature and Zeroth Law
Maxwell defined the temperature of a system as its Thermal state considered with reference to its ability to communicate heat to other bodies.
When a hot body is brought into contact with a cold body, the hot body becomes cooler and the cold body becomes hotter. After sufficient time, the temperature of both the bodies will be equal. At that point, the two bodies are said to have reached thermal equilibrium.
Consider three bodies A, B and C. If the bodies A and B are in thermal equilibrium with C when brought into contact separately, they are also in thermal equilibrium with each other. This concept is known as zeroth law of thermodynamics.
Several properties of materials are found to be varying with temperature in a predictable way. This variation is used to measure temperature. In mercury thermometers, expansion of mercury with temperature is used for temperature measurement.
BASIC CONCEPTS AND DEFINITIONS
Thermodynamics is the science of energy transfer which deals with the relations among heat, work and properties of systems.
The name ‘thermodynamics’ is derived from the Greek words therme, meaning ‘heat’ and dynamis meaning power. Thus, thermodynamics is basically the study of heat and power.
Application Area of Thermodynamics
Energy transfer is present in almost all the engineering activities. Hence, the principles of thermodynamics are playing vital role in designing all the engineering equipments such as internal combustion engines, rockets, jet engines, thermal and nuclear power plants, refrigerators etc.