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Thermodynamics and its laws.

Updated on April 6, 2013

Entropy Vs Temperature Curve of Carnot cycle


How did the thermodynamics came!!

"Thermodynamics" this word came from two word "Therm" is a Greek word means "Heat" and "Dynamics" means "speed" or velocity or any thing in motion. So the total meaning of this word Thermodynamics is the study of "heat in Motion" although it discuss abut on only heat also pressure and velocity and temperature e.t.c.

Though it is focused on Heat transition and motion it has vast field which created lots of different subjects too!! Like Heat transfer, Refrigeration, Automobile Engineering, Air Conditioning, Aero Dynamics, Jet Propulsion related subjects all are connected to Thermodynamics by many different way. So we can call it mother of all those subjects.

The Laws of Thermodynamics are may now looks very simple but all have came through many years of practice and experiments. The story of Zeroth law is very interesting. This was described at the last when all of the three laws was already explained and accepted. Then It came, but it was the most simple one that's why it was named as Zeroth laws!!

Laws and Discussion

There are 4 laws those are the basic of Thermodynamics and as well the refrigeration, automobile engine or IC (Internal Combustion i.e petrol engine, diesel engine e.t.c ) engine and Air-conditioning.

Zeroth LAW: It is the simplest law and anyone can understand it very easily. It states that "If 2 body (let's take A and B) are in thermal equilibrium with and other body (let's take it as C) then those two bodies (A and B) are also at thermal Equilibrium with each other.
if we write it in a mathematical form then the relation is like that A=C and B=C then A=B. Isn't it simple!!

1st Law: Its a bit harder than the zeroth law. It's about the relation between Work and Heat. It states that "The work-done(let's take it as W) of a system is proportional to the heat supplied(let's take is as Q ) to the system." Now if we write the statement in Mathematical form then the relation is Q∞W. Simply we can tell that the heat is converted to the work through the system, but every system has some loss i mean there is no system which has 100% efficiency. So we can again write the formula Q=W+E ,where E is the energy loss by the system. This law also state that the Heat and Work can be converted vice-versa. But Work is called High grade energy. So there is always larger heat amount necessary to produce a specific amount of work. Because there is some loss. I think that's enough to clarify this law.

2nd LAW: Its the most Complicated law among all the laws in Thermodynamics. But we can state is simpler form like this "Its impossible to supply heat from a cold body to a hot body without some extra effort or some External Agent". This law has many type of Explanation but i think my statement is the simplest one. Hope it will help to understand these think more easily. From this Law the Heat Pump and Refrigeration system was invented as the refrigeration system is the "external agent" !!!

3rd LAW: Its also not simple though it seems, but this law requires to Know the term "Entropy". Its a term used to define the internal energy level of a system. This law States "Its impossible to reduce the total entropy of a system." Though It may seems contradicting with many thermodynamic cycle's because most of them has a step of reducing the entropy. But the fact is in a Cycle the Total Entropy is constant, mainly it rely on the temperature and pressure. When the pressure reduces the total volume increases as a result the sp. entropy reduces. Some Thermodynamics cycles are added to give you some clear idea what i said.

Hope i have made some clear explanation of those laws and i will keep adding things. If you have any questions i will glad to answer and discuss over it.

Volume Vs Pressure Curve of Carnot Cycle



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