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Optoelectronic sensors

There are so many devices that are sensitive to light, and so many applications for them, that we are devoting a separate chapter to the optoelectronic sensors.

Light-dependent resistor

This consists of a disc or square block of semiconducting material, usually cadmium sulphide, with two electrodes printed on its surface (photograph above). The electrodes are shaped so that there is a narrow gap between them, but their edges are waved to make the length of the gap as great as possible. The whole is encapsulated in clear plastic. When a p.d. is applied to the electrodes, a current passes from one electrode to the other.

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