Concept of Temperature:

The temperature is thermal state of body which describes the degree of hotness or coldness of body. If the two bodies are brought in contact, heat will flow from hot body at higher temperature to cold body at lower temperature.

Temperature is thermal potential causing flow of heat energy. It is intensive thermodynamic property independent of size and mass of the system. The temperature of a body is proportional to stored molecular energy that is the average molecular kinetic energy of molecules in a system. (A particular molecule does not have temperature, it has energy. The gas as system has temperature).

Instruments for measuring the ordinary temperatures are called as thermometers and those for measuring high temperatures are called as pyrometers.