The second law of thermal dynamics has been variously described by different scientists. Of these, the statements of Planck , Kelvin and Clausius are the most famous. These are discussed below: 1. Carno's statement: It is not at all possible to build a device capable of fully converting a certain amount of heat energy into mechanical energy. 2. Planck's statement: It is not possible to build an engine in a corner that will absorb heat from an object and turn it into work endlessly while the corners of the environment will not change. 3. Classia Ser statement: It is not possible for an automatic device to transfer heat from a low temperature object to a high temperature object without the help of external energy. 4. Kelvin's statement: It is not possible to get an uninterrupted supply of energy by cooling an object from the coldest part of its surroundings.