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Practical physics: external photoeffect

No matter how average the average person was in his everyday life from the school program that he had passed, it does not, and will make you remember. This is exactly what happens when it comes to the appearance of an external photoelectric effect.


A photoelectric effect in physics is usually considered to be the alignment of electrons in atoms, molecules of a substance that arises and occurs under the influence of light. And the external photoelectric effect is a process in which electrons are knocked out by the light with such force that they fly out beyond the outer limits of their substance.

A bit of history and practice

For the first time this amazing fact drew the attention of the physicist from Germany Heinrich Hertz in the distant 1887th year. The study of the discovery was continued by Herz's colleague, the Russian physicist Stoletov. A brilliant Einstein developed a theory of photoelectric effect based on the ideas of quantum physics. Since then, the external photoelectric effect has been studied quite deeply and versatile, and the knowledge gained is used in full in the development and production of photocell-based instruments. If we take the most elementary example, then this is an automatic garage gate, working on photocells.

Mechanisms of this type operate on electrical energy. However, photocells, which use only the external photoelectric effect, transform the energy received by radiation into an electric one not completely. Therefore, to use them as sources of electricity there is no special sense, which can not be said about automation. It is with the help of light beams that the electrochains are controlled in automatic mechanisms.

Without exaggeration, it can be argued that the discovery of the photoelectric effect has become a truly revolutionary event in physics. Here are the most significant consequences:

  • Before the scientists, the mystery of the nature of light, the light ray, was revealed;
  • Cinema from the mute became "talking", the ways of voice-over were invented, and the very fact of transferring a moving image was also made possible by the photoelectric effect;
  • Creation on the basis of photoelectronic devices of such machines and "smart machines", which, in accordance with given parameters without the participation of a person, produce various details;
  • Many different mechanisms based on the work of photoelectronic automation.

Thus, the photoeffect itself and its application have become a kind of breakthrough in modern technology.

Classification of photocells

Photo effects are divided into several types depending on their properties and functions.

  1. External photoeffect (in another way - photoelectron emission). Electrons that fly outside the substance when it occurs are called photoelectrons. And the electric current, which they form when they move in an orderly manner along the external electric field, became known as a photocurrent.
  2. An internal photoelectric effect that affects the photoconductivity of a substance. It occurs when electrons are redistributed across semiconductors and dielectrics, depending on their energy state and the aggregate state - solid or liquid. The phenomenon of redistribution occurs under the influence of light. It is then that the electrical conductivity of the substance increases; The photoconductivity effect is obtained.
  3. Valve photoelectric effect - the transition of photoelectrons from their bodies to other solids (semiconductors) or liquid (electrolytes).

The external photoelectric effect is the basis for the work of modern vacuum photocells. They are made in the form of glass flasks, in which the inner surface is partially covered with a thin layer of metal sputtering. The insignificant thickness of the layer provides a small working yield. The transparent window of the bulb lets in light, and the anode located inside it in the form of a wire loop or disk catches photoelectrons. If the anode is connected to the positive pole of the battery, the circuit will close and an electric current will flow through it. Those. Vacuum photocells can switch the relay on or off.

By combining photocells and relays, you can create different "seeing" machines, for example, a subway machine.

Thus, being the basis of many production processes, the external photoelectric effect as a great physical discovery has become the key to the successful operation of industrial automation.

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