What is the basis of a thermocouple ?

• A. A pair of dissimilar metal wires
• B. Two strands of the same metal
• C. One strand of nylon with one strand of metal
• D. Two strands of pvc

Answer: (A)

Thermocouples rely on the Seebeck effect: when two dissimilar metals are joined at a junction and there is a temperature difference between that junction and the other ends, a small voltage is generated. The different metals have different tendencies to move electrons with temperature, so electrons diffuse at different rates and an electromotive force appears. This voltage changes with temperature, allowing measurement.

If the metals were the same, there’s no difference in their electron behavior at the junction, so essentially no measurable voltage is produced. Insulating or non-conductive materials like nylon or PVC don’t form the required metal-metal junction, so they can’t generate the thermoelectric signal.