Describe Thomson Effect Of Evolution Of Heat ?
Thomson’s effect was discovered by Thomson (later called Kelvin). According to this effect, if two parts of a single conductor are maintained at different temperatures, an e.m.f. is developed between them. The e.m.f. so produced is called Thomson’s e.m.f. If the steady current is passed through an unequally heated conductor, an absorption or evolution of heat in excess of Joule’s heat, takes place in the conductor. Thus Thomson’s effect is the absorption or evolution of heat in excess of Joule heat when current is passed through an unequally heated conductor. Thomson effect is reversible effect. To understand Thomson’s effect, consider an unequally heated rod AB of copper. Let the end A of the be at higher temperature than its end B. on passing the current from A to B in the rod, heat is evolved along the length of the rod. In case, the current is passed in the rod from end B to A, the heat is absorbed along the length of the rod. It is accounted due to the fact that in case of copper, the hot end of the rod is at higher potential and its cold end is at lower potential. When current flows from hot end to cold end of copper rod i.e. from higher potential to lower potential, the energy is produced which is radiated out in the form of heat. When current is flowing from cold end to hot end of the copper rod i.e. from lower potential to higher potential, the energy required which accounts for the absorption of heat energy
