Final answer:
The distance between the hot and cold junctions of a thermocouple should be determined by the need to measure temperatures accurately and safely, rather than by a specific length.
Step-by-step explanation:
The distance between the hot and cold junctions of a thermocouple is not strictly determined by a maximum length in terms of feet or meters. Rather, it is essential that the hot junction be placed where it needs to be to accurately measure temperatures, such as inside a furnace, while keeping the cold junction at a reference temperature, often at room temperature. The performance of a thermocouple is not generally inhibited by the length of the wire between the junctions unless the wires are very long, which could lead to signal degradation or noise.
Therefore, the hot junction should be positioned as needed for safe and accurate temperature readings, and the actual answer to this question would be option a. This consideration ensures that the temperature differential (ΔT) can be measured effectively to provide accurate thermal readings for various applications, including maintaining optimal temperatures in homes or mechanical systems.