Final answer:
Two dissimilar metals are needed in a thermoelectric circuit because they have different Seebeck coefficients, which results in a net voltage when subjected to a temperature difference. This voltage loop drives an electrical current, necessary for practical applications like power generation or temperature measurement.
Step-by-step explanation:
The reason we need two dissimilar metals for thermoelectric materials is that they have different Seebeck coefficients—a property that quantifies the voltage created when there is a temperature difference across the material. This difference in coefficients leads to a net voltage across the circuit made from these two dissimilar metals when there is a temperature gradient. To understand this, consider that metals can exhibit a voltage in the presence of a temperature gradient even when they're made from a single material. However, in order to exploit this effect to drive an electrical current, which can be used for power generation or temperature measurement (like in a thermocouple), it is essential to create a thermoelectric circuit.
In a thermoelectric device, a temperature gradient causes electrons to move from the warmer side to the cooler side in each metal, which establishes a voltage. If the metals are dissimilar, they will develop different voltages in response to the same temperature difference because of their different Seebeck coefficients. When these two metals are connected at two junctions kept at different temperatures, the different voltages create a net voltage loop that drives the current through the circuit.
To address heat conduction, this property depends on the transfer of kinetic energy from hotter to cooler molecules. In the context of a metal being cooled by water or ice (as in the provided reference question 47), the substance with the higher specific heat capacity (like water) will absorb more heat for the same temperature change than the substance with the lower specific heat (like ice), hence cooling the metal more effectively.
As a result, while a single metal can conduct heat and exhibit a Seebeck effect individually, two dissimilar metals, connected in a closed loop, are necessary for establishing a thermoelectric circuit that can be practically utilized for generating electricity or measuring temperature.