How does a thermocouple generate an electrical current?

A thermocouple generates an electrical current through the principle of thermoelectricity, which is based on the junction of two different metals. When these two metals are joined together and exposed to a temperature differential—where one junction is heated and the other is kept at a different temperature—an electromotive force (EMF) is created.

This phenomenon is known as the Seebeck effect. In a thermocouple, when the temperature at one junction increases (the hot junction), it creates a voltage difference due to the varying rates at which the two metals conduct electricity in response to that temperature change. This voltage can then be measured as an electrical current.

In this context, the generation of current stems from the effects of heating rather than the act of welding or magnetic separation, which do not produce the conditions necessary for determining a voltage via temperature differences. The correct answer directly emphasizes the role of heating two welded metals together, allowing the thermoelectric effect to take place efficiently.