How does a thermocouple work?

• A. As temperature changes, electrical resistance changes, the difference in current flow is converted to temperature
• B. It measures pneumatic pressure
• C. It uses light to gauge temperature
• D. It stores a charge proportional to heat

Answer: (A)

Two different metals joined at one end produce a voltage when their temperatures differ. This is caused by the Seebeck effect: heat creates a flow of electrons between the two metals, generating a small electrical voltage that is proportional to the temperature difference between the hot junction and the reference junction. The thermocouple itself doesn’t rely on measuring resistance or current changes, nor does it use light or store a charge. A high-impedance instrument reads the tiny voltage (in millivolts) and, knowing the reference temperature, converts that signal into an actual temperature reading. Different metal combinations (types) yield different sensitivities, but the fundamental idea remains the same: a temperature difference creates a measurable voltage.