Zeroth law of Thermodynamics

Zeroth law of Thermodynamics: The 'zeroth law' states that 'if two bodies (say A and B) are in thermal equilibrium with another body C, then the bodies A and B will also be in thermal equilibrium with each other'. This law is important as it helps in understanding the concept of temperature.

Explanation: For example, If A is in thermal equilibrium with B and C, then B is in thermal equilibrium with C. This means that all three are at the same temperature, and it forms a kind of ground for comparison of temperatures. It is called the Zeroth Law because it precedes the First and Second Laws of Thermodynamics.




Zeroth Law of Thermodynamics and Thermometers

The below is an sample problem is for Zeroth Law of Thermodynamics

Question: In a constant-volume gas thermometer how can you measure temperature by measuring the pressure of the gas?


Answer: When a gas is heated the pressure increases if it is restricted to a fixed volume. When a gas is cooled the pressure decreases at constant volume. This effect is used to measure temperature by measuring the pressure of the gas when it is placed in thermal contact with the substance whose temperature is being measured. If the pressure of a gas in a constant-volume thermometer is plotted versus temperature a straight line is obtained. If you extend the line down to zero pressure you find the temperature at this point to be -273.15 degrees Celsius.