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Photocell, how photocells work

Photocell, or photoelectric cell, uses the photoelectric effect. A photocell usually consists of some form of semiconductor material. A popular material is selenium. How photocells work? Selenium gives an electric potential that varies as the brightness of the light falling upon it varies.

Photocells (or silicon photodiode) are sometimes used in burglar alarms. The selenium or similar material is mounted in a glass container and connected in some way with an alarm circuit. An invisible infra-red beam shines on it. If an intruder enters the room, he breaks the beam: it no longer illuminates the photocell and so the electrical potential of the selenium changes and sets off the alarm.

How photocells work? - Sputnik satellite is powered by silicon photodiode

How photocells work?

This Sputnik satellite is powered by photocells.

There are other semiconductor materials that generate a voltage when a light shines on them. Photographers' light-meters often use materials of this sort. The voltage generated increases as the brightness of the light increases. It drives a current through a small meter which shows the light value. The more sensitive type uses cadmium sulphide or silicon, whose electrical resistance varies with the intensity of light.

Materials like these are used to power many of the artificial satellites and space probes sent up by the United States and Russia. Large numbers of individual cells are arranged around the body of the satellite or are mounted on 'paddles' that extend out from the satellite and are kept pointing towards the Sun, which supplies the light.

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