GITAM, Department of Engineering Physics


Third law of Thermodynamics

            Second law of thermodynamics asserts that complete conversion of heat into work by any device whatever, is impossible. According to the efficiency equation of a Carnot engine, complete conversion is theoretically possible when T2 = 0K, ie., when the low temperature reservoir is reduced to absolute zero temperature.

            A fundamental feature of all cooling processes is that the lower the temperature , the more difficult it is to go still lower. This experience in the march towards absolute zero has led to the formulation of the third law of thermodynamics. It is stated one form in the following way.

            “It is impossible by any procedure whatsoever, no matter how idealized, to reduce any system to the absolute zero of temperature in a finite number of operations. In other words, it is impossible to attain 0K.”

            Nernst’s theorem treats the third law of thermodynamics in terms of entropy. On the basis of experiments conducted at low temperatures, W.Nernest concluded that, “ at 0K, any change in the state of a system takes place without a change in entropy.” This is called the Nernest’s theorem which is some times called the third law of thermodynamics.