What is a thermocouple composed of?

A thermocouple is a temperature sensor that operates on the principle of thermoelectric effect, which occurs when two dissimilar metals are joined together. When these two metals are bonded at one junction and exposed to different temperatures at the other junction, a voltage is generated that is proportional to the temperature difference. This voltage can then be measured and converted into a temperature reading.

The uniqueness of thermocouples comes from the fact that it specifically requires dissimilar metals to create the potential difference necessary for accurate temperature readings. Different metals have different thermoelectric properties, which enables the thermocouple to function effectively across a range of temperatures. The other choices do not align with this principle: similar metals would not create the required voltage difference, a single metal alloy would not provide the necessary junction effects, and multiple metals mixed together do not achieve the direct electrical interactions needed for thermoelectric generation. Thus, only the bonding of two dissimilar metals is appropriate for constructing a thermocouple.