Which one of the following transducers requires power supply for its operation?ThermocouplePhotovoltaic cellPiezoelectric crystal Thermistor

The transducer that requires power supply for its operation is the Thermistor.

Here's why:

1. Thermocouple: It does not require a power supply. It works on the principle of the Seebeck effect, which states that a voltage difference is created when two dissimilar metals are joined at two junctions and one junction is heated more than the other.

2. Photovoltaic cell: It also does not require a power supply. It works on the principle of the photovoltaic effect, which states that when light (photons) hits a material, it can cause the material to emit electrons, creating a voltage difference.

3. Piezoelectric crystal: It does not require a power supply either. It works on the principle of the piezoelectric effect, which states that when mechanical stress or strain is applied to a material, it generates an electric charge.

4. Thermistor: It requires a power supply for its operation. A thermistor is a type of resistor whose resistance changes significantly with temperature. It needs a power supply to measure the change in resistance, which can then be used to calculate the temperature.