UNDERSTANDING THERMAL EQUILIBRIUM
When two bodies A and B, which are at different temperatures, are placed in contact with each other , heat is transferred form the hotter body, A to the colder body B.
The temperature of the body A decrease as a result of loss of heat from its particles while the temperature of the body Y increases when its particles receive heat. When the temperatures of both bodies, A and B are equal, thermal equilibrium has been reached.
Ex:
A(80˚C) contact with B(50˚C)
After few minutes
A(65˚C) contact with B(65˚C)
The two bodies, A and B are said to be in thermal equilibrium if the rates of heat transfer from A to B, and vice versa, are equal –i.e. the net rate of heat transfer between the two bodies is zero.
Two bodies which are in thermal equilibrium are at the same temperature irrespective of their shapes, mass, sizes or type of surface.
*Characteristic thermal equilibrium was happen:
# Rates of heat transfer between the two bodies are equal.
# Temperatures of the two bodies are equal.
Change In The Physical Properties Of Material With Temperatures
The physical property of a substance which is sensitive to and varies linearly with temperatures change of the material is known as thermometric property.
All substance in the solid, liquid or gaseous phase will undergo change in physical properties when heat energy is absorbed or released by the particles in the matrial.
An important application of the thermometric property of a substance is the construction of the thermometer to measure temperature.
Measurement Of Temperature Using The Principal Of Thermal Equilibrium
The most effective instrument for the measurement of temperature is the thermometer.
All thermometers use the thermometric properties of specific substance to measure temperature.
Various types of thermometers are constructed based on the four thermometric properties of substance that are sensitive to change in temperature.
Four thermometric properties:
Gas thermometer- physical property which varies with temperature-Gas pressure
Mercury thermometer- physical property which varies with temperature-Volume of mercury
Resistance thermometer- physical property which varies with temperature-Electrical resistance of platinum
Thermocouple thermometer- physical property which varies with temperature-Electrical potential different (e.m.f.) between the two junction of two dissimilar metal wires
