What principle explains the behavior of dissimilar metals at a junction when heated?

The thermoelectric effect explains the behavior of dissimilar metals at a junction when heated. This principle is based on the generation of an electric voltage when two different metals are joined and exposed to a temperature difference. When one junction is heated while the other is maintained at a lower temperature, charge carriers in the metals move from the hot side to the cold side, creating a voltage. This phenomenon is utilized in thermocouples, where the output voltage is proportional to the temperature difference, allowing for temperature measurement and sensing.

In contrast, the other principles listed do not directly apply to this scenario. Electromagnetic induction involves the generation of electric current through changing magnetic fields, which is not relevant to the behavior of metals at a heated junction. The photoelectric effect describes how light can cause the emission of electrons from a material, an entirely different process that does not involve thermal behavior at metal junctions. Lastly, chemical bonding pertains to the interactions between atoms to form molecules, which is unrelated to the temperature effects on different metals at a junction.