 Welcome back Mechanically Ice. The second law of thermodynamics was very essential in defining the direction of a process. This makes us wonder, what is the second law of thermodynamics? We will explore it as a four-part series. Now there are two statements of the second law of thermodynamics. First is the Kelvin Planck statement. It states, it is impossible for a heat engine to produce network in the complete cycle if it exchanges heat only with bodies at a single fixed temperature. Second is the Clausius statement, which states it is impossible to construct a device which operating in a cycle will produce no effect other than the transfer of heat from the cooler to a hotter body. Before we establish the equivalence of these theorems, we need to define a few terms. The first among them is a thermal energy reservoir, which is defined as a large body of infinite heat capacity capable of absorbing or rejecting an unlimited quantity of heat without suffering appreciable changes in its thermal condition. Second is the concept of heat engine, defined as a thermodynamic cycle in which there is a net heat transfer to the system and net work transfer from the system. Third is the concept of refrigerator and heat pump. The former is a device which when operating in a cycle maintains the body at a temperature lower than that of the surroundings. The later is a device which operating in a cycle maintains a body at a temperature which is higher than that of the surroundings. Hence we just saw that the second law of thermodynamics has two statements that is the Kelvin Planck and the Clausius statements. And we'd also define some basic terms namely a thermal energy reservoir, a heat engine, a refrigerator and heat pump. 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 help the channel grow. So here are the top mechanical EIs of our last videos. In the next episode of Mechanical EI, find out how the equivalence of Clausius and Kelvin Planck's theorem is achieved.