A thermocouple is made from copper and iron. At the hot junction, the current
A. flows from copper towards iron.
B. flows from iron towards copper.
C. flow decreases.
D. flow increases.

Hint: Thermocouple, also referred to as a thermoelectric thermometer, thermo junction, or thermal, is a device for measuring temperature that is made of two wires connected at either end and constructed of different metals.

Complete step by step solution:
The temperature to be measured is placed at one junction, while the other junction is maintained at a constant lower temperature. The circuit has a measurement device linked to it. The Seebeck effect, which develops as a result of the temperature difference between the two junctions, is an electromotive force that is roughly proportionate to the temperature difference. Either conventional temperature tables or a calibrated measuring device can be used to read temperature.

The covalency of an element—or whether it will give out or absorb electrons—determines the positive and negative terminals of a thermocouple. Iron will lose the electron to copper because copper is more electropositive, while iron will gain it. As a result, current would move from copper to iron.

So the correct answer is option A.

Additional information: The thermoelectric effect can occur in any two dissimilar metals or metal alloys, but only a select handful are employed as thermocouples, such as antimony and bismuth, copper and iron, or copper and constantan (a copper-nickel alloy). High-temperature thermocouples often use platinum, either alone or in an alloy with rhodium.

Note: Thermocouple types are designated by the metals used to produce the wires, such as type E (nickel, chromium, and constantan), type J (iron and constantan), type N (two nickel-silicon alloys, one of which contains chromium and magnesium), or type B (a platinum-rhodium alloy). Due to its broad operating temperature range (about$200\text{ to }1,{{260}^{{}^\circ }}\text{C}\left[ 300\text{ to }2,{{300}^{{}^\circ }}\text{F} \right]\text{ }$) and low cost, type K (nickel-aluminum and nickel-chromium wires) is the most popular.