The photoelectric effect is the physics of the phenomenon

In 1887 the German scientist Hertz discovered the influence of light on the electrical discharge. While studying the spark discharge, Hertz discovered that if the negative electrode is illuminated with ultraviolet rays, the discharge begins at a lower voltage on the electrodes.

It was further discovered that when the light of an electric arc is illuminated by a negatively charged metal plate connected to an electroscope, the arrow of the electroscope is lowered. This indicated that the metal plate illuminated by the electric arc loses its negative charge. The metal plate does not lose its positive charge when illuminated.

The loss of metallic bodies when they are illuminated by light rays of negative electric charge is called the photoelectric effect or simply the photoelectric effect.

The physics of this phenomenon has been studied since 1888 and the famous Russian scientist AG Stoletov.

The study of the photoelectric effect Stoletov produced using an installation consisting of two small disks. The continuous zinc plate and thin mesh were placed vertically against each other, forming a capacitor. Its plates were connected to the poles of the current source, and then illuminated by the light of an electric arc.

Light freely penetrated through the grid to the surface of a solid zinc disk.

Stoletov established that if the zinc coating of the capacitor is connected to the negative pole of the voltage source (is a cathode), then the galvanometer included in the circuit shows the current. If the cathode is a grid, then there is no current. Hence, the illuminated zinc plate emits negatively charged particles, which determine the existence of a current in the gap between it and the grid.

Stoletov, studying the photoelectric effect, the physics of which was not yet revealed, took for his experiments disks from a wide variety of metals: aluminum, copper, zinc, silver, nickel. Attaching them to the negative pole of the voltage source, he observed how an electric current appeared in the circuit of his experimental installation under the action of an arc. Such a current is called a photocurrent.

As the voltage between the capacitor plates increases, the photocurrent increases, reaching a maximum value at a certain voltage, called the saturation photocurrent.

Investigating the photoelectric effect, the physics of which is inextricably linked with the dependence of the saturation photocurrent on the magnitude of the light flux incident on the cathode plate, Stoletov established the following law: the magnitude of the saturation photocurrent will be directly proportional to the light flux incident on the metal plate.

This law is called Stoletov.

Later it was established that the photocurrent is a stream of electrons torn out by light from a metal.

The theory of photoelectric effect has found wide practical application. So devices have been created based on this phenomenon. They are called photocells.

The photosensitive layer-the cathode-covers almost the entire inner surface of the glass bottle, except for a small window for light access. The anode is a wire ring, reinforced inside the balloon. In the tank - a vacuum.

If you connect the ring to the positive pole of the battery, and the photosensitive metal layer through the galvanometer with its negative pole, then when the layer is illuminated, a current appears in the circuit as the proper light source.

It is possible to turn off the battery completely, but even then we will observe a current that is only very weak, since only a negligible fraction of the electrons ejected by light will fall on the wire ring-anode. To increase the effect, a voltage of the order of 80-100 V is needed.

The photoelectric effect, the physics of which is used in such elements, can be observed using any metal. However, most of them, such as copper, iron, platinum, tungsten, are sensitive only to ultraviolet rays. Alkaline metals alone - potassium, sodium and especially cesium - are also sensitive to visible rays. They are used to make photocell cathodes.