What does a thermocouple do?

A thermocouple is a temperature sensor that operates based on the principle of thermoelectricity. When two different metals are joined together at one end and heated, they generate a voltage that is proportional to the temperature difference between the hot junction (where the two metals are joined and exposed to heat) and the cold junction (the point where the junction is connected to a measuring instrument). This voltage can be measured and interpreted to give an accurate reading of temperature.

The other options describe different measurement devices: measuring pressure differences pertains to pressure sensors, measuring humidity levels relates to hygrometers, and measuring electrical current involves ammeters or similar devices. While each of these instruments serves distinct purposes, they do not measure temperature directly, which is the specific function of a thermocouple.