SOLUTION

PHOTOCONDUCTIVE CELLS

• A photoconductor is a bulk semiconductor device, whose resistance varies inversely when the light is incident on its surface.
• All semiconductors can be considered photoconductors.
• This is because any semiconductor will produce electron-hole pairs (EHP) when it is irradiated by electromagnetic radiation of the optical frequencies.
• These include frequencies in the infrared, visible and ultraviolet radiations. 

• The photoconductive cell is a  two-terminal semiconductor device whose resistance varies inversely with the intensity of light that falls upon its photosensitive material.
• These devices are also called photoresistive cells or photoresistors since the change in conductivity appears as a change in resistance.