Zeroth Law Of Thermodynamics


The zeroth law is one of the best laws of Thermodynamics. I discuss the Zeroth Law Of Thermodynamics in this article.  Here I also write the application of zeroth law and some other topics about zeroth law. So read this article and out quarries in your mind. So don’t worry I explain all about zeroth law.
It is developed much later than the other 3 laws. Due to some confusion about the nomenclature, the zeroth law develops later. The complication shows because the new law gave a clear definition of temperature.

Before discussing all zeroth laws first know what is zeroth law?

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Zeroth Law Of Thermodynamics :

It is one of the four laws of thermodynamics. It is invented by Ralph H. Fowler.
This law state that :
  “if two systems are at an equal time in thermal equilibrium with a third system. Then all three systems also thermal equilibrium with each other”.

For Example :
If an object ‘A’ is thermal equilibrium with another object ‘B’. Also individually in thermal equilibrium with an object ‘C’. Then objects ‘B’ and ‘C’ will also thermal equilibrium with each other. This statement clarifies the Zeroth Law Of Thermodynamics. This law is established on temperature measurement.

Zeroth Law Of Thermodynamics
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 In the Zeroth Law Of Thermodynamics temperature is something worth measuring.  Because it indicates whether the heat will switch between objects or not. This is a true view of how the objects interact. Actually, if two objects are not in physical contact. Heat still can flow between them by utilizing the radiation mode of heat transfer.  If the systems are in thermal equilibrium heat is not flow. Zeroth’s law clarifies that.

More information about Zeroth Law Of Thermodynamics :

This law appears very understandable and it is so essential that we call it a law. This law is named after three laws. It provides fundamentals for the other three laws. So that it is named Zeroth Law Of Thermodynamics.

Reason for called the Zeroth Law Of Thermodynamics :

It is named so because the first two laws of thermodynamics were founded before. They were named before. The zeroth law was more essential than the other laws of thermodynamics. But It was delayed to find that. It is the reason why it is named/called the Zeroth Law Of Thermodynamics.

How does Zeroth’s law lead to the concept of temperature?

The Zeroth Law Of Thermodynamics permits us to introduce the theory of temperature. The temperature measures the hotness or coldness of a body. All bodies in thermal equilibrium are selected at equal temperatures. So the temperature of the two bodies concludes the direction of heat flow. It happens when the two bodies are in contact.

Which coordinate is introduced by the Zeroth Law Of Thermodynamics?

The function t(→x) is called the empirical temperature. This is a temperature measured by gas thermometers. The zeroth law clarifies the theory of temperature. Once it is specified, we can choose n+1 variables (→x, t) as the thermodynamic coordinates of the body.

Thermal Equilibrium :

The criteria for Thermal equilibrium is the equivalence of temperatures. Temperature is the main property in the thermal equilibrium process. This property can compare between hot and cold. Two or more bodies at various temperatures into contact after some time.  They meet a common temperature. They are said to exist in thermal equilibrium.

Significance of Zeroth Law Of Thermodynamics :

Mathematical theories always need a relation called an equivalence relation. A way of announcing whether two things are the same or not. The zeroth law is the equal relation of thermodynamics. Because it gives for the mathematical theory of temperature. It helps the existence of physical thermometers.

The variation between energy and temperature is a key theory. It is not enough to know which way heat will flow and when they are put in contact. It is the comparative temperatures of the two systems. It establishes the direction of heat flow.

But how can temperature be measured?

Generally, a thermometer is an object. It shows and calibrated properties depending on its temperature. Example – Mercury expands in volume in a specific way as it heats up. A thermometer is a thermal equilibrium with an object. Then identify those properties. Such as how much the mercury has increased.

The implication of the zeroth law can be seen. When attempting to compare the temperatures of two objects. If a thermometer is fixed in liquid A.  It comes to be in thermal equilibrium with that liquid. It reads a specific temperature.

If the thermometer is placed in liquid B, it increases thermal equilibrium. It reads the same temperature as A In thermal equilibrium. The zeroth law allows us to say liquid A and liquid B are the same temperatures.

Applications of Zeroth Law Of Thermodynamics with Examples :

The law is valuable for the mathematical formulation of thermodynamics. It is more particularly for stating the mathematical description of temperature. This law is generally used to compare the temperatures of various objects.

If we want to measure the proper temperature, a reference body is required. A certain factor of that body changes with temperature. The change in that factor may be taken as a sign of a change of temperature. That selected factor is known as thermodynamic property.

Anyway, the most popular application of the Zeroth Law Of Thermodynamics is thermometers. We can know the zeroth law in an effort by taking a very common thermometer. It has mercury in a tube. As the temperature is increased this mercury expands since the area of the tube is steady. Due to this growth, the height is increased. Now, the increased height of the mercury label shows the temperature changes. It helps us to measure it.

Furthermore, I give another example of the Zeroth Law Of Thermodynamics. When you have two glasses of water. One glass has hot water and the other has cold water. Now if we leave them at the table for a few hours. They will accomplish thermal equilibrium with the temperature of the room.


Zeroth Law Of Thermodynamics is a statement. Mention that this law is about thermal equilibrium. The thermal equilibrium implies that systems have the same temperature and conversely systems. It has a similar temperature are in thermal equilibrium.

Zeroth Law Of Thermodynamics
Image Credit – Maschen

Also ReadFirst Law of Thermodynamics

Also ReadBest 6 Limitations of First Law of Thermodynamics and its Applications

Also Read4 Best Examples of Open System in Thermodynamics

My thoughts about Zeroth Law Of Thermodynamics :

This law gives a clear definition of temperature to the other three laws. I explained all about zeroth’s law. I discuss some more information about the Zeroth Law Of Thermodynamics. I think I explain your quarries in this article.

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