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Zeroth Law of Thermodynamics

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  • Last Updated : 16 Nov, 2022
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Zeroth Law of Thermodynamics states that when two bodies are in thermal equilibrium with another third body then the two bodies are also in thermal equilibrium with each other. Ralph H. Fowler developed this law in the 1930s, many years after the first, second, and third laws of thermodynamics had achieved widespread acceptance. Here Thermal Equilibrium implies that when two systems are in contact with a barrier permeable only to heat, so there will be no change or transfer of heat. Let’s learn more about Zeroth’s Law of Thermodynamics in this article!

Zeroth Law of Thermodynamics

Consider two systems A and B, separated by a wall that does not allow any exchange of energy between them. Such a wall is known as an insulating wall or adiabatic wall. The third system C is separated from systems A and B by a conducting or diathermic wall as shown in the figure.

Zeroth Law of Thermodynamics

 

Since energy can be exchanged between systems A and C, both A and C are in thermal equilibrium. Similarly, energy can be exchanged between the systems B and C, so both B and C are also in thermal equilibrium. In other words, both systems A and B are in thermal equilibrium with the third system C separately. When the adiabatic wall between systems A and B is removed, no transfer of energy takes place between them. This shows that systems A and B are also in thermal equilibrium with each other. This observation leads to an important law known as Zeroth law of thermodynamics which is stated as follows:

Zeroth Law of Thermodynamics states that when two bodies are in thermal equilibrium with another third body then the two bodies are also in thermal equilibrium with each other.

According to Zeroth’s law of thermodynamics, if system A is in thermal equilibrium with system C, then:

Zeroth's law of thermodynamics

 

Temperature of System A = Temperature of System C

Similarly, if system B is in thermal equilibrium with system C, then

Temperature of System B =Temperature of System C

Now, from the above relation, we have 

Temperature of System A = Temperature of System B

Thermal Equilibrium

The zeroth law of thermodynamics recognizes that temperature is a valuable measurement since it predicts whether or not heat will flow between things. Regardless matter how the items interact, this is true. Heat can move between two things even if they are not physically interacting, as per the radiation method of heat transmission.

The zeroth law of thermodynamics says that no heat flow will occur if the systems are in thermal equilibrium.

Thermodynamics is distinguished from other studies by temperature. This trait is capable of distinguishing between hot and cold. When two or more bodies of different temperatures come into touch, they eventually reach a similar temperature and are said to be in thermal equilibrium. 

Application of Zeroth Law of Thermodynamics

The law is crucial for the mathematical formulation of thermodynamics, or, to put it another way, for expressing the mathematical definition of temperature. The most common use of this concept is to compare the temperatures of different things. If we want to accurately measure temperature, we’ll need a reference body and a characteristic of that body that changes with temperature. The change in that characteristic could be interpreted as a temperature change. The chosen feature is referred to as a thermodynamic property.

Nonetheless, Thermometers are the most prevalent application of the zeroth law of thermodynamics. Using a simple thermometer with mercury in a tube, we may witness the zeroth law in operation. Because the area of the tube remains constant as the temperature rises, the mercury expands. The height has grown as a result of this development. Now, the variation in the height of the mercury label indicates temperature changes and, in essence, aids us in measuring it.

Depending on their thermometric characteristic, several types of thermometers can be utilized. The following is a list of thermometers 

  • Constant pressure gas thermometer – Volume
  • Constant volume gas thermometer – Pressure
  • Electrical resistance thermometer – Resistance
  • Mercury-in-glass thermometer – Length
  • Thermocouple – Thermal e.m.f.

When you have two glasses of water, you have another illustration of the zeroth law of thermodynamics. One glass will be filled with hot water, while the other will be filled with cold water. If we leave them on the table for a few hours, they will achieve thermal equilibrium with the room’s temperature.

FAQs on Zeroth Law of Thermodynamics

Question 1: What is the Zeroth Law of thermodynamics?

Answer:

According to the Zeroth Law of Thermodynamics, two systems that are in thermal equilibrium with a third system separately are also in thermal equilibrium with each other.

Question 2: Write the Significance of the Zeroth Law of Thermodynamics.

Answer:

The Zeroth Law of Thermodynamics provides a significant relationship which is very helpful for the mathematical formulation of thermodynamics. It mathematically transforms the relationship between systems’ thermal equilibrium into an equivalence relation, which can represent the equality of a particular quantity related to each system.

Question 3: What is the difference between Heat and Temperature for a System?

Answer:

The Difference between Heat and Temperature for a System can be given as:

  • Heat is a form of energy that is transferred between two bodies because of a temperature difference existing between them.
  • While Temperature may be defined as the thermal condition of a body that determines the direction of heat flow i.e. it determines whether the body will receive heat from another body or it will give heat to the same. 

Question 4: Body A comes into contact with body B, which then comes into contact with body C. A has a higher temperature than B, which is higher than C. According to the Zeroth Law of thermodynamics, what is the proper flow direction?

Answer:

If a body with a higher temperature comes into touch with a body with a lower temperature, the higher temperature body will transfer heat to the lower temperature body. As a result, heat will travel from point A to point B to point C, eventually reaching the same temperature.

Question 5: What is the Internal Energy of a System?

Answer:

Internal energy is the sum of all forms of energy stored in atoms or molecules.

Question 6: Which scale can be created from the Zeroth Law of Thermodynamics?

Answer:

Celsius Scale can be created from the Zeroth Law of Thermodynamics which is used In most part of the world. That gives water’s freezing point at 0 degrees and boiling point at 100 degrees at mean sea level.

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