Which device uses dissimilar metals to control electron flow?

Which device uses dissimilar metals to control electron flow?

• A. RTD
• B. Diode
• C. Thermocouple
• D. Thermistor

Answer: (C)

Two different metals joined together produce a voltage when there’s a temperature difference between the ends. This thermoelectric effect, called the Seebeck effect, is what a thermocouple uses: the junctions of dissimilar metals generate an electrical potential that varies with temperature, so connecting the hot and cold junctions to a circuit lets current flow if the circuit is closed. That reliance on dissimilar metals to create a signal is the distinguishing feature here. The other devices operate by different principles. An RTD changes its resistance with temperature in a single metal, so you measure temperature by resistance rather than by generating a voltage from metal differences. A diode uses a semiconductor p-n junction to control current flow, not a pair of metals producing a thermoelectric voltage. A thermistor also changes resistance with temperature, typically using a ceramic semiconductor material rather than dissimilar metals.

Two different metals joined together produce a voltage when there’s a temperature difference between the ends. This thermoelectric effect, called the Seebeck effect, is what a thermocouple uses: the junctions of dissimilar metals generate an electrical potential that varies with temperature, so connecting the hot and cold junctions to a circuit lets current flow if the circuit is closed. That reliance on dissimilar metals to create a signal is the distinguishing feature here.

The other devices operate by different principles. An RTD changes its resistance with temperature in a single metal, so you measure temperature by resistance rather than by generating a voltage from metal differences. A diode uses a semiconductor p-n junction to control current flow, not a pair of metals producing a thermoelectric voltage. A thermistor also changes resistance with temperature, typically using a ceramic semiconductor material rather than dissimilar metals.