What device produces electricity when two different metals are heated together?

The device that produces electricity when two different metals are heated together is known as a thermocouple. A thermocouple operates based on the thermoelectric effect, specifically the Seebeck effect, which occurs when two dissimilar metals are joined at two junctions. When there is a temperature difference between these junctions, an electromotive force (EMF) is generated, which can be measured as voltage.

Thermocouples are commonly used in temperature measurement and control applications due to their ability to convert thermal energy into electrical energy effectively. They are reliable, rugged, and can operate over a wide range of temperatures, making them an essential tool in industrial process control.

In contrast, other devices listed serve different functions. A transducer converts one form of energy into another, but not specifically focused on the generation of electricity from heat in the manner that a thermocouple does. A resistor is a passive component that resists current flow and does not generate electricity. An oscillator produces a repetitive signal, often for timing or frequency generation, but does not relate to the thermoelectric effect. Thus, the thermocouple is the correct choice for the described function.