Which device emits a voltage when heated or cooled?

The correct device that emits a voltage when heated or cooled is a thermocouple. Thermocouples consist of two different types of metal wires joined at one end, and when this junction is subjected to a temperature difference, it generates a voltage proportional to the temperature differential. This phenomenon is based on the Seebeck effect, which allows thermocouples to serve as temperature sensors in various applications.

In contrast, a thermistor, while it does change resistance with temperature, does not generate a voltage directly in response to temperature changes. Instead, it is typically used in conjunction with other components to measure temperature. Resistors and capacitors have different functions: resistors are used to limit current or divide voltages, and capacitors store electrical energy in an electric field, neither of which involves generating a voltage due to temperature changes. Thus, thermocouples are specifically designed for temperature measurement and voltage generation in response to thermal changes.