What principle does a thermocouple rely on to measure temperature?

• A. The Peltier effect
• B. The Seebeck effect
• C. The Hall effect
• D. The Joule heating principle

Answer: (B)

Thermocouples measure temperature through the Seebeck effect: when two dissimilar metals are joined and there’s a temperature difference between the junctions, a small voltage is generated in the circuit. The voltage is proportional to the temperature difference, so by reading the voltage with a suitable reference and calibration, temperature can be determined. The Peltier effect is the heating or cooling that occurs at a junction when current flows—essentially the reverse phenomenon of Seebeck and not the signal used for sensing. The Hall effect produces a voltage perpendicular to current and magnetic field and is used for magnetic field sensing, not temperature measurement. Joule heating is the heat produced by current in a conductor and does not provide the temperature-dependent signal a thermocouple relies on.