Zeroth Law Of Thermodynamic: The Thermal Equilibrium Law
• So the first is the Diathermic wall- "A Diathermic wall is a wall that allows the easy exchange of heat between two bodies (or between two systems or between system and surrounding) but does not allow the exchange of mass between them". This means that it is a good conductor of heat. It is sometimes called as metallic wall because it is made of metal.
• While the other is the adiabatic wall- "An Adiabatic wall is that wall which neither allows exchange of heat nor mass between two systems (or between system and surrounding)". Since there is no exchange of heat and mass between the system and its surroundings, the system remains insulated from its surroundings.
➛ That's why whenever we separate the two systems by an adiabatic wall, then there is no concept of equilibrium between them. But whenever we separate these two systems through diathermic wall then the concept of thermal equilibrium comes between them and we can get thermal equilibrium between both the systems when both the systems are insulated from the surrounding.
With the help of these two types of wall, we will understand the concept of zeroth law of thermodynamics.
Zeroth Law Of Thermodynamic
Since, we know that heat transfer takes place only between systems that are separated by a diathermic wall. Therefore system 'A' cannot interact with system 'B' as they are seperated by an adiabatic wall, but system 'A' can interact with system 'C' and similarly system 'B' can interact with system 'C'. But only and only in the form of heat transfer.
As we know that heat always transfer from higher temperature system to lower temperature system, i.e., heat can transfer from system 'A' to system 'C' or from system 'C' to system 'A' and similarly, heat can transfer from system 'B' to system 'C' or from system 'C' to system 'B'. And the heat continues to transfer until the temperature of the two systems becomes the same ,i.e., after some time system A will be in thermal equilibrium with system C and system B with system C. As a result, system A will also be in thermal equilibrium with system B.
But why does this happen? How will system A be in thermal equilibrium with system B?
This situation can be well explained by the statement of zeroth law of thermodynamics.
GENERAL STATEMENT
The zeroth law is very important which gives the definition of temperature or it shows that some physical quantity named “Temperature” also exist. Consider three systems A, B and C. Zeroth law of thermodynamics states that- “When two systems (say system 'A' and system 'B') are in thermal equilibrium with a third system (say system 'C'), then according to this law those three systems will also be in thermal equilibrium with each other”. Thus, in the above figure all the three systems will be in thermal equilibrium with each other.
Mathematically, these situation can be represented as; If, Ta = Tc and Tb = Tc, then according to zeroth law of thermodynamics Ta = Tb. Where Ta, Tb and Tc are the temperatures of system A, B and C respectively.
.......“Zeroth law of thermodynamics tells us about the concept of temperature. And this law was actually developed after the first and second laws of thermodynamics”.........
EXAMPLES OF ZEROTH LAW
(a) All three blocks obtained thermal equilibrium.
Block A is in contact with block C and block B is in contact with block C. But block A and B are not in contact with each other.
Even though, after some time all the three blocks will reach the same temperature. (In other words, these three blocks achieves thermal equilibrium with each other)
(b) Hot Coffee Becomes Cold After Some Time.
Because the hot coffee is surrounded by the cold air of the room. This hot coffee loses its heat to the surrounding air of the room. Hot coffee will keep on losing the heat until its temperature becomes equal to the temperature of the surrounding air of the room. As a result, the example of a hot coffee cup illustrates the zeroth law of thermodynamics.
History Of Zeroth Law Of Thermodynamics
I was wandering why it is named “Zeroth”, why not first, second, third, etc???
It should be like first law, second law, third law, etc… But it is named zero. Why?
The name “Zeroth law” was invented by Ralph H. Fowler in the 1930s, long after the first, second, and third laws were widely recognized.
Amazingly, all the three laws of thermodynamics were already discovered before 1930s without defining “Temperature”.
Fowler realised that thermal equilibrium is very important phenomenon and it should be defined before 1st law of thermodynamics. This law could not be referred to as the fourth because it is the most fundamental of all the others. The zeroth law of thermodynamics has an interesting name because of this.
The second reason was that there were already so many books published with the First Law, the Second Law and the Third Law. So changing the number of these laws can cause a lot of confusion. Thus he was forced to adopt the number “Zero” for his law. Finally this law was named “Zeroth Law Of Thermodynamics”.
The law of thermal equilibrium, the zeroth law is an important law in thermodynamics. Despite such importance, this law was not fully realised for soo long, until 1935, when Fowler and Guggenheim, wrote it as;
…..we introduce the postulate, “If two assemblies are each in thermal equilibrium with a third assembly, they are in thermal equilibrium with each other”……
This law is a crucial mathematical method for understanding thermodynamics.
....The “Transitive relationship law” is another name for it.....
What Did You Find From The Zeroth Law Of Thermodynamics?
We discovered that there is one physical characteristic that tells us whether or not the bodies are in thermal equilibrium based on the zeroth law of thermodynamics. And that physical property is “TEMPERATURE”.
.......“If the temperature of the bodies are same, then the bodies are in thermal equilibrium with each other”.......
In simple words, we can state that the 0th law of thermodynamics helps us in determining the body's temperature.
Application Of Zeroth Law Of Thermodynamics
1) To measure human body temperature (You have definitely experienced this when you had fever. 0th law of thermodynamics helps us in finding the temperature of a human body.)
2) To measure atmospheric temperature.
3) Temperature measurement for industrial applications.
4) Temperature measurement in air conditioners (To maintain the temperature of the room, the thermometer measures the temperature of air inside the room and accordingly the air conditioner works based on the load inside the room)
5) Temperature measurement in refrigerator (The refrigerator also uses thermometer to check the inside space temperature of the refrigerator and accordingly it maintains the temperature)
6) In food processing industries (To regulate the temperature in food processing industries, thermometers are used, which note down the temperature of the room or particular area. And then further cooling as let requirements)
THERMAL EQUILIBRIUM
Thermal equilibrium exists when the temperature of two bodies is the same. As “Heat is the flow of energy from a body of higher temperature to a body of lower temperature, provided that the bodies are connected”. When this gradient balances out and no further transfer of heat energy takes place, this condition is termed thermal equilibrium.
If two bodies Y and Z are in thermal equilibrium with a third body X, the bodies Y and Z are thus in thermal equilibrium with each other as well.
FAQs
How Thermometer Measures The Body's Temperature????
When a thermometer is kept in contact with a human body suffering from fever, the mercury gains heat and it expansion in the thermometer tube. After few seconds, mercury achieves thermal equilibrium with the human body. At this condition, the temperature of thermometer will be same as the temperature of human body. And we can measure the readings on the thermometer.
Thus in this way, zeroth law of thermodynamics is used to find the body temperature using thermometer.
Hope you have found this article helpful!!
Let me know what you think about ZEROTH LAW. Feel free to comment if you have any queries.!!
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