Simple Law of Thermodynamics – All four laws

Thermodynamics is a branch of Physics that deals with the thermal state for gas system and other macroscopic systems. There are four laws of Thermodynamics – Zeroth Law, First Law, Second Law and Third Law of Thermodynamics. Sometimes, most of the students feel difficulties to understand these laws. In this post, I am going to explain all four laws of Thermodynamics in a simple way.

Simple Law of Thermodynamics

1. Zeroth Law of Thermodynamics

The Zeroth Law of Thermodynamics states that if any two thermodynamic systems are in thermal equilibrium with a third thermodynamics system, then these two systems will also be in thermal equilibrium with each other.

Let, three thermodynamic systems A, B and C. If A is in thermal equilibrium with C and B is in thermal equilibrium with C, then according to Zeroth law, A and B will be in thermal equilibrium with each other.

Click here for the detailed post on Zeroth law of Thermodynamics.

2. First Law of Thermodynamics

The 1st Law of Thermodynamics states that if some amount of heat is given to a thermodynamic system, it will use some parts of heat to increase its kinetic energy and works with rests of heat. Here, heat is equivalent to energy.

Let, dQ amount of heat is supplied to a system. Its increase in internal energy is dU and amount of work done by the system is dW. The, according to the First law, dQ = dU + dW.

Click here to read the 1st Law of Thermodynamics in details.

3. Second Law of Thermodynamics

There are two statements for the 2nd law of Thermodynamics –

Clausius Statement:

According to Clausius statement, No self-acting machine can transfer heat from a reservoir of lower temperature to another reservoir of higher temperature.

So, a system need some external work to transfer heat from cold body to hot body.

Kelvin-Planck’s Statement:

According to Kelvin and Planck’s statement, No self-acting machine can convert some amount of heat into work entirely.

So, some amount of heat will be lost during conversion of heat into work.

4. Third Law of Thermodynamics

The 3rd law of Thermodynamics states that at absolute zero temperature the entropy of a perfect crystal is zero. That means there will be no entropy of a perfect crystal at a temperature of zero Kelvin.

These are the four simple laws of Thermodynamics. This is all from this article. If you have any doubt on this topic you can ask me in the comment section.

Thank you!

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  1. 1st Law of Thermodynamics – in details

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