# Zeroth Law of Thermodynamics

Thermodynamics is an important concept both for students to score and science to explore but many people find this concept of thermodynamics, specially laws of thermodynamics tough. Good thing being there is one law in out of all these laws of thermodynamics which is easy as well as important to understand as well.

Therefore in this article, we will be covering zeroth law of thermodynamics. This is fourth law of thermodynamics but there was so much confusion while naming this law about whether it should called the fourth law or by some other name. This confusion was there because, this laws gives more clear explanation of temperature compare to other three laws of thermodynamics.

In the end, it was called as “Zeroth law of thermodynamics” which gives the base idea of  temperature and thermal equilibrium. Don’t worry I know these terms sound confusing but it will all get clear by the end of the article.

## What is Zeroth law of thermodynamics ?

Zeroth law of thermodynamics states that, when two system are in thermal equilibrium with the third one then all three are in thermal equilibrium with each other. Now this can be confusing when you first read it, but actually it is not.

This statement just says that, if body ‘A’ is in thermal equilibrium with body ‘B’ and body ‘B’ is in thermal equilibrium with body ‘C’ then body ‘A’ will also be in thermal equilibrium with body ‘C’ and all three will be in thermal equilibrium with each other.

Zeroth law can be explained in many different ways but the most simplest would be “Systems in thermal equilibrium has the same temperature”

### Thermal equilibrium:

We are using term “Thermal Equilibrium” a lot in the explanation but what exactly is this thermal equilibrium?

Thermal equilibrium is a condition when two different bodies of different temperature attains a same temperature as time passes. Temperature is a unique property, which can help us to measure whether a body is hot or cold.

When these two bodies, of different temperature are brought near each other, as time passes both bodies will have same temperature and this is called as thermal equilibrium.

Explaining thermal equilibrium in language of science is little tricky. Two bodies are said to be in thermal equilibrium when there is no transfer of heat between the two.

### Example and uses of zeroth law of thermodynamics:

Practice use is necessary of any law we learn and the same goes for zeroth law of thermodynamics as well.

Thermometer is one of the common example of  zeroth law of thermodynamics. With increase in temperature, mercury present inside it expands but due to area being constant, height is expanded and label around it shows us the temperature. This is one of the most common application of zeroth law of  thermodynamics.

Application of zeroth law of thermodynamics can also be seen in food  processing industry, refrigerators, temperature measurement in various industries and to measure atmospheric temperature