Photoconductive cell
The electrical resistance of a semiconductor depends on the intensity of the incident light. A photoconductive cell works on the above principle.
A photoconductive cell consists of a thin transparent surface film of some metal, which is placed on thin layer of semiconductor like selenium, which in turn is placed over a metal layer of iron. A high potential difference is applied across surface film and iron layer. When light of suitable frequency falls on the transparent film, the electrical resistance of selenium layer decreases. This changes the current flowing in the circuit.
