Second Law of Thermodynamics

Second law of thermodynamic is one of the major law from three laws of  thermodynamic.

Thermodynamic is word come from root word thermo which mean heat and dynamic which mean power. Law of thermodynamics are the law of heat power. All things in universe obey law of thermodynamics.

Check All three law of thermodynamics :

First law of thermodynamics – First law of  thermodynamics knows as the law of conservation of matter, which states that “  Energy /Matter cannot be created and nor can it be destroyed . It can change from one phase to another phase with keeping total energy in the universe constant”.

Second law of thermodynamics:

The Second Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time. The second law also states that the changes in the entropy in the universe can never be negative.

“Entropy” is defined as a measure of non usable energy within a closed system (take universe as an example). Entropy increases with increases in unusable energy.

The second law of thermodynamic give more information about the heat process.

“Heat never flow itself from colder body to a hotter body”. Thermodynamic law also used to determine the theoretical performance of engineering system like heat pump, heat engine .

Kelvin –plank  statement of the second law of thermodynamic:

“it’s impossible to convert complete heat power into equal amount of work”

Its impossible for any devices as a heat engine that operate on cycle to receive heat from a single reservoir and produce net amount of work


Lets take example:

Second law of thermodynamic


Fig No.1 show that 100% heat energy Q=100kj  is converting into Q=100kj work . Which not follow second law of thermodynamic.

Fig .No.2 follow second law of thermodynamic which show “complete amount of heat is not converting into work , there is some heat losses in the form of friction etc”.

Clausius law of second law of thermodynamics

“ Its impossible to construct a device which transfer heat from low temperature body to high temperature body without external power.”

Its mean heat cannot flow from cold body to hot body without any work input.

Second law of thermodynamic

Perpetual motion machine (PMM2):

Perpetual motion machine is a machine which never stop . If you created one perpetual motion machine and set it going , it would be keep on going until you stop . device that operates with PMM2 absolutely no energy loss.

Second law of thermodynamic

The PMM2 machine violate the second law of thermodynamic . Practically its impossible to convert complete heat energy into work .

The efficiency of PMM2  is


N is 100% for PMM2.


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