What type of thermometer uses two dissimilar metals joined together to measure extreme temperatures?

The thermometer that utilizes two dissimilar metals joined together to measure extreme temperatures is known as a thermocouple. This instrument operates based on the principle of thermoelectricity, where when the junction of the two metals is heated or cooled, it generates a voltage that is correlated to the temperature difference between the junctions. This makes thermocouples highly suitable for measuring a wide range of temperatures, including very high or extreme temperatures, which is an essential characteristic in many industrial and scientific applications.

In contrast, other types of thermometers such as fluid-in-metal thermometers and alcohol thermometers rely on the expansion or contraction of a fluid contained in a glass tube to measure temperature changes, which limits their ability to accurately measure higher temperature ranges. Thermographs also do not measure extreme temperatures in the same manner as a thermocouple; rather, they record temperature changes over time using various mechanisms, often making them less direct and less suitable for extreme conditions compared to thermocouples.