## Zeroth Law of Thermodynamics – Class 11 | Chapter – 12 | Physics Short Notes Series PDF for NEET & JEE

Zeroth Law of Thermodynamics: The zeroth law of thermodynamics is one of the fundamental principles of thermodynamics, and it states that:

“If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.”

This law establishes the concept of temperature and thermal equilibrium, and it provides a basis for understanding the behavior of heat energy in systems and the way in which energy is transferred from one system to another.

The zeroth law is called the “zeroth” law because it was added to the other laws of thermodynamics after the first, second, and third laws had already been established. The law was recognized as an important principle of thermodynamics because it provides a way to define temperature, which is a fundamental concept in thermodynamics.

The zeroth law is important because it allows us to measure temperature and to compare the temperatures of different systems. By establishing the concept of thermal equilibrium, the law also provides a framework for understanding the way in which energy is transferred between different objects and environments.

Overall, the zeroth law of thermodynamics is a fundamental principle of thermodynamics, and it is essential for understanding the behavior of heat energy in systems and the way in which energy is transferred from one system to another.

## Example of Zeroth Law of Thermodynamics

An example of the zeroth law of thermodynamics is when two objects are placed in contact with each other and reach thermal equilibrium.

For instance, consider two cups of water: Cup A and Cup B. Cup A has a temperature of 80°C, and Cup B has a temperature of 50°C. When the two cups are placed in contact with each other, heat energy will flow from Cup A to Cup B, as the hotter water loses energy to the cooler water. Eventually, both cups will reach the same temperature, and they will be in thermal equilibrium with each other.

According to the zeroth law of thermodynamics, if Cup A is in thermal equilibrium with a third cup of water, Cup C, and Cup B is also in thermal equilibrium with Cup C, then Cup A and Cup B must be in thermal equilibrium with each other. This means that the temperatures of Cup A and Cup B will be equal when they are in contact with each other, as the law states that systems in thermal equilibrium with a common third system are in thermal equilibrium with each other.

In other words, if Cup A and Cup B are both in contact with Cup C and Cup C has the same temperature as Cup A, then Cup B will also have the same temperature as Cup A when the two cups are in contact with each other. This example demonstrates the zeroth law of thermodynamics in action, as it shows how thermal equilibrium is established between two objects that are initially at different temperatures, by bringing them into contact with each other and a third system.

## Application of Zeroth Law Of Thermodynamics

The zeroth law of thermodynamics has a wide range of applications in various fields, some of which are:

• Temperature measurement: The zeroth law provides a basis for the measurement of temperature, as it establishes the concept of thermal equilibrium and the idea that systems at the same temperature are in thermal equilibrium with each other.
• Thermal insulation: The zeroth law is important in the design of thermal insulation systems, which are used to prevent heat transfer between two systems. By maintaining a temperature difference between two systems, insulation systems can be used to prevent heat from flowing between them, and the zeroth law can be used to ensure that the insulation is effective.
• Refrigeration systems: The zeroth law is also important in the design of refrigeration systems, which are used to cool objects or environments. By using a refrigerant to extract heat from an object or environment, the refrigeration system can maintain a temperature difference and prevent heat from flowing back into the object or environment.
• Thermal management in electronics: The zeroth law is used in thermal management of electronic devices to ensure that they do not overheat. By monitoring the temperature of electronic components and using heat sinks or other cooling systems to maintain a temperature difference, the zeroth law can be used to prevent overheating and ensure that the electronic devices operate efficiently.

Overall, the zeroth law of thermodynamics is a fundamental principle of thermodynamics, and it has numerous applications in various fields, from temperature measurement and thermal insulation to refrigeration systems and thermal management in electronics.

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