Welcome back McGangeliye. A very essential part after the second law of thermodynamics is the concept of entropy. This makes us wonder what is entropy. To know more about how the Kevin Planck's in Clausius Seatman's equivalence is achieved, check out the second part. Now, in this third part of the series, we begin with the Carnard's theorem. Carnard's theorem states that of all the engines operating between a given constant temperature source and a given constant temperature sink, none has an efficiency higher than a reversible engine. Also, Clausius theorem states that the cyclic integral of dQ upon t for a reversible cycle operating between two equilibrium states i and f is equal to 0. This integral can be replaced as a sum of two integrals, one each for r1 and the other for r2, which can be rearranged as r1 equals negative of r2. Since r2 is a reversible path, we can simply flip the equation while changing the negative sign. Since r1 and r2 represent any two reversible paths, so the equation for r is independent of the reversible path connecting i and f. That is, there exists a property of a system whose value at a final state minus its value at an initial state is equal to r. This property is called entropy and is denoted by s. Hence, we learnt about what the Carnard and Clausius theorem is. Then we went on to find out what entropy is and why it is a property of the system. So, like, subscribe and comment with your feedback to help us make better videos. Thanks for watching. Also, thanks a lot for those constructive comments. You helped the channel grow. So here are the top mechanical ears of our last videos. In the next episode of Mechanical EI, find out what are the applications of entropy principle.