The first step to study Seebeck effect is to understand the physics of thermocouple. Thermocouple is a thermoelectric device made of two dissimilar metals connected at two points.
Suppose one side of two connected copper wires is hotter than the other(Fig. 1.1). Since
copper is a metal, its electrons are free to move. The electrons diffuse from the hot side to
the cold side. When a voltmeter placed between two side, it detects no voltage difference
because the electrons diffuse uniformly.