Nate Electrical Practice Exam

What happens to resistance when photons of light strike a cadmium sulfide photoconductive cell?

1. Resistance increases

2. Resistance decreases

3. Cell produces voltage

4. None of the above

The correct answer is: Resistance decreases

When photons of light strike a cadmium sulfide photoconductive cell, the energy from the photons excites electrons in the material, causing them to move from the valence band to the conduction band. This process effectively creates free charge carriers (electrons and holes) in the material. As the number of free charge carriers increases, the material becomes more conductive, which means the resistance of the photoconductive cell decreases. In a photoconductive cell, this decrease in resistance allows more current to flow when the material is exposed to light, making it highly sensitive to changes in illumination. This property is utilized in various applications such as light sensors and photodetectors. Thus, the overall effect of light on the resistance of a cadmium sulfide photoconductive cell is a decrease in resistance, confirming the accuracy of the chosen answer.