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# Laws of Thermodynamics

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 Sub Topics The branch of physics which deals with the relation between the heat and mechanical work is defined as thermodynamics. It is concerned with the properties of systems composed of many particle such as a gas, liquid or solid. The thermodynamics here is concerned with the mutual conversion of heat and also the mechanical work. It also deals with the interactions between the objects. The subject matter of thermodynamics is based on three experimental laws, namelyThese laws are based on experimental facts but not on theoretical facts. The laws provide criteria for predicting the feasibility or otherwise of a process and the energy transformations that occur in the process. In this section we will learn more about laws of thermodynamics.

## Zeroth Law of Thermodynamics

There are four laws of thermodynamics, beginning with the “zeroth” law. The need for the zeroth law become apparent after the others were developed and the law is a statement about the concept of temperature.
When two bodies A and B are separately in thermal equilibrium with a third body C, then A and B are in thermal equilibrium mutually, i.e., If $T_{A} = T_{C}$ and $T_{B} = T_{C}$ then $T_{A} = T_{B}$

## First Law of Thermodynamics

The first law of thermodynamics is based on the principle of conservation of energy, which states that the energy cannot be created or cannot be destroyed but it can be transformed from one form to another. It state that the change in the internal energy of a thermodynamic system is equal to the amount of energy added by heating the system excluding the amount lost due to the work done by the system on its surroundings. It also state that the energy is conserved in any process in the thermodynamic system and its surroundings.Let us take $dU$ is the change in internal energy, $dQ$ be the heat added to the thermodynamic system and $dW$ be the work done, then the first law of thermodynamics written as

$dQ = dU + dW$