What do photoelectric cells do

The emitter is connected to a negative terminal and the collector is connected to the positive terminal of a battery. Radiation of frequency more than the threshold frequency of material of emitter is made incident on the emitter. Photo-emission takes place. The photo-electrons are attracted to the collector which is positive w.

Thus current flows in the circuit. If the intensity of incident radiation is increased the photoelectric current increases. Applications of the Photoelectric Cell:. The photoelectric cell is used in the reproduction of sound which is recorded on a movie film. In a movie, film sound is recorded on the film of actions in the form of a thin transparent strip. This thin transparent strip is called the soundtrack. The transparency of the soundtrack depends on the variation of the frequency of sound recorded.

Using photocell sound is reproduced from the soundtrack. When the film is run in a projector the light of the projector this soundtrack and falls on the photocell. Due to variation in the soundtrack, the variation of intensity of sound takes place and thus the photo-electric current varies. The current is amplified and is fed to speakers. Use of Photoelectric Cell in Burglar Alarm:.

The photovoltaic cell is used in a burglar alarm. This device is kept near a safe to be protected from a thief. A burglar alarm is a device which is used for locating intruder, thief near precious, valuable things like safe. The device consists of a photocell and an infrared source of light.

The light from the infra-red source is made continuously incident on the photocell making photoelectric effect continuous. Thus the photoelectric current in the cell flows continuously. When the path of infra-red light is obstructed by the thief, the light falling on photocell is cut-off and photo-electric current in the cell stops and relay circuit is activated and a siren starts hooting.

Use of Photoelectric Cell in Exposure meter:. The Columbia Electronic Encyclopedia, 6th ed. All rights reserved.

See more Encyclopedia articles on: Electrical Engineering. Enter your search terms:. The most common type consists of two electrodes separated by a light-sensitive semiconductor material. A battery or other voltage source connected to the electrodes sets up a current even in the absence of light; when light strikes the semiconductor section of the photocell, the current in the circuit increases by an amount proportional to the intensity of the light. In the phototube, an older type of photocell, two electrodes are enclosed in a glass tube—an anode and a light-sensitive cathode, i.

Although the phototube itself is now obsolete, the principle survives in the photomultiplier tube, which can be used to detect and amplify faint amounts of light.

In this tube, electrons ejected from a photosensitive cathode by light are attracted toward and strike a positive electrode, liberating showers of secondary electrons; these are drawn to a more positive electrode, producing yet more secondary electrons—and so on, through several stages, until a large pulse of current is produced.