Recall this……..!
Hello dear students, we are familiar that heat is transferred from point of higher temperature to lower temperature till the difference between the two points is zero. If you consider some day to day examples like mixing of hot water and cold water for taking bath, you must have noticed that the temperature of hot water decreases as its heat is absorbed by the cold water. The exchange of heat is continued till both of them attain the same temperature, we called this condition as thermal equilibrium.
Then the thermal equilibrium is the condition of two systems in thermal contact with each other and they do not transfer any heat amongst them.
To explain the conditions of thermal equilibrium the law termed as Zeroth law is very useful. It is called Zeroth law as it was introduced after first and second law of thermodynamics.
Let’s understand the law in detail……………!
Consider the following thermodynamic systems P, Q and R as shown in the fig.1) below.
Now suppose that the systems P and Q are in thermal equilibrium, also systems P and Q in thermal equilibrium, and then we can say that the systems Q and R are also in thermal equilibrium.
Hence the Zeroth law of thermodynamics is stated as, “If two systems are each in thermal equilibrium with third system, they are also in thermal equilibrium with each other”.
Consider the following examples…..!
- When you go to doctor for complaining of fever, then he checks our body temperature using thermometer. The temperature of thermometer rises till our body and thermometer attains the thermal equilibrium.
- A cup of hot tea kept on table gets cools down, and attain the temperature which is same of room temperature. i.e. tea and room atmosphere are in thermal equilibrium.
Some important points to note…..!
- Temperature measuring science is known as ‘thermometry’.
- Temperature of system is measurable quantity and can be measured with thermometers in different scales like Celsius, Fahrenheit, and Kelvin etc.