Laws of thermodynamics

Laws of thermodynamics:

There are actually four laws of thermodynamics. These laws are very important and are considered in every aspect of engineering related to thermodynamics and it's applications. These laws are on the basis of every day life and many modern technologies are based on these applications.

Zeroth law of thermodynamics: 

 Zeroth law states that if two bodies are in thermal equilibrium with a third body  then they’re in thermal equilibrium with each other.

From the above image if A is connected to B and are in thermal equilibrium with each other and body B is connected to C and are in thermal equilibrium with each other then both A and C are in thermal equilibrium with each other. 

First law of thermodynamics:

This law is also stated as Conservation law of energy.

This law states that the heat and mechanical work are mutually convertible. According to this law a definite amount of heat is converted to a definite amount of  work and loss of heat due to increase in internal energy and overcome friction losses and vice versa.

This law states that energy can neither be created nor destroyed. Though it can be transformed from one form to another. According to this law, the energy due to heat supplied(Q) must be balanced by the external work done(W) plus the gain in internal energy (E) due to rise in temperature. In other words 

Q = W + E

Second law thermodynamics:

This law is also stated as law of degradation energy .

This law states that there is a definite limit to the amount of mechanical energy, which can be obtained from a given quantity of heat energy. 

According to clausius this law states that "It is impossible to transfer heat from body at lower temperature to a body at a higher temperature without the aid of an external energy for a self acting machine in a work process." 

According to Kelvin plank this law states that "It is impossible to construct a engine whose sole purpose is to convert heat energy into work." Extracting heat and using it all do work would constitute an ideal engine which is forbidden by second law of thermodynamics.

Third law of thermodynamics:

This law states that entropy of a system remains constant when the system attains zero Kelvin or absolute zero(0K or -273C).