Photoelectric cell

A photoelectric cell and/or. Photoelectric cell is a radiation detector. It counts in as much to the electron tubes as itself also with it in an evacuated glass container an anode and a cathode (photocathode) finds.

The photocathode consists of a metal (e.g. Cesium with particularly small electron affinity),from by light electrons to be set free can (outside photoelectric effect). <p>

Fotozelle, Länge ca. 90mm; die Anode ist ein Drahtbügel, die Foto-Kathode wird durch den rückseitig innen mit Metall beschichteten Glaskolben gebildet
Photoelectric cell, length approx. 90mm; the anode is a hook, which photocathode by back inside the glass bulb coated with metal is

formed between anode (+) and cathode (-) a tension put on, then becomethe electrons to the anode, set free by the light, accelerated, an electric current (photo stream) can be measured. If the tension put on is small, then the photo stream is proportionally to the tension put on, the porportionality factor depends on the exposure intensity. This photo stream goes with higher tensions into a saturationover, i.e. the river does not continue to rise with further increase of the tension put on. This is because of it that with small tensions the electrical field strength is not sufficient, in order all electrons resulted from the photoelectric effect at the cathode toward anode to accelerate and thus to the photo streamcontribute to leave. However it can naturally flow no more electrons between cathode and anode than by the light to be set free why the saturation arises. Even if no voltage supply is connected with the photoelectric cell, cathode forms with exposure a tension out between anode andthe anode loads itself negatively up. This tension is proportionally to the frequency of the irradiated light and can for the determination Planck 'schen quantum of action to be used. The tension is formed, because the light (sufficient high frequency and thus energy presupposed) drives electrons out from the photocathode.These electrons possess an energy, which corresponds to the difference between quantum energy of the light and electron affinity of the electron made of the cathode metal. The free electrons meet (partly) also the anode and load these negatively. Thus an electrical tension between the electrodes is formed. Further one Electrons must go through now the training electrical field, in order to hit the anode, to which they need energy. Finally the tension is so largely that the energy of the again extracted electrons is not sufficient any longer, the plate to reach - the tension remains constantly.< p>

Demarcation:from semiconductors developed photo receivers rank it among the semiconductor detectors, e.g. are. Photodiodes or solar cells - these are not called photoelectric cells.


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