When current is passed through a wire, maintaining its two endsat different temperatures heat will be either evolved or absorbed between the two points. This effect is called Thomson’s Effect. It is a reversible process. The amount of heat absorbed or evolved in this effect is directly proportional to the amount current passing through it. If heat will be evolve when current is passed from high temperature to low temperature, then the element have positive(+ve) Thomson’s coefficient otherwise negative(-ve) Thomson’s coefficient.
Cause of Thomson’s effect:
If the two ends of a wire is maintained at different temperature, they will be at different electric potential. In this case if current is passed from high potential to low potential, heat will be evolved otherwise absorbed.