What does a thermocouple output depend on?

• A. The color of the insulation
• B. The physical length of the circuit
• C. The temperature difference between the hot junction and the reference junction
• D. The flow rate of the surrounding air

Answer: (C)

The output of a thermocouple comes from the Seebeck effect: when two dissimilar metals are joined, they generate a voltage that is determined by the temperature difference between the hot junction and the reference (cold) junction. The magnitude and polarity of that voltage depend on how hot the hot junction is relative to the reference, and on the metals used.

So the intrinsic thermoelectric signal is set by the temperature difference between the two junctions. Choices like insulation color don’t affect the emf, and the physical length of the circuit mainly introduces lead resistance rather than changing the thermoelectric voltage. Air flow can influence the actual temperatures by cooling, but the output voltage itself reflects the difference between junction temperatures, not the flow rate.