What is the photoelectric effect

In the modern world, the photovoltaic effect is used almost everywhere: alarms, solar panels, sensors, etc. Let's find out about such a discovery in more detail.

The history of the discovery of the photoelectric effect

The photoelectric effect was discovered at the end of the 19th century, namely in 1887 by the scientist G. Hertz, who discovered during an experiment that a spark discharge between zinc balls skips much more easily when one of the balls is illuminated with ultraviolet light.

In the same year A. G. Stoletov found out that the charge released under the action of light has a negative sign.

In 1898, Lenard and Thomson found that the charge of particles, which is taken out of matter by the action of a light flux, is equal to the specific charge of an electron.

As you can see, the discovery aroused genuine interest in the scientific community and almost immediately raised a huge number of fundamental questions.

And all because at that time no theory could explain this effect in any acceptable way.

Of course, the classical theory of metals did not forbid the light flux to knock electrons out of the metal.

According to classical reasoning, electromagnetic waves could well "wash out" electrons from the structure metal in the same way as the sea waves raise to the surface and beat various materials.

The only problem was that the photo effect could not be explained so easily, and here's why:

1. The electrons appeared almost instantly after the process of irradiation of the metal with a light flux was started.
2. As it turned out, the photoelectric effect appeared even at the weakest light flux, and with an increase in the irradiation intensity, the energy of the "washed out" electrons remained unchanged.
3. The photo effect is practically inertialess.
4. Each substance has its own lower limit of the photoelectric effect. This is the frequency at which this effect is still observed.

These factors did not fit into the classical vision of the interaction of light with electrons.

The solution to these problems was found by the famous physicist A. Einstein at the very beginning of the 20th century. Moreover, the solution he found gave a serious impetus to the development of quantum mechanics.

So, shortly before Einstein's discovery, another scientist, Max Planck, demonstrated that black body radiation can be describe, assuming that atoms can both emit and absorb light in certain energy portions - quanta.

Planck put forward the assumption that such a phenomenon is due to the specific structure of the atom, and not the nature of light.

And now Albert Einstein put forward the theory that the light itself is distributed in so-called portions, which are called photons.

In this case, photons have a dual nature and can behave as a particle and a wave.

So, when interacting with an electron, a photon can behave like a particle, and, roughly speaking, literally knock an electron out of its atomic orbit.

If we draw an analogy, then the association with the collision of two billiard balls is best suited.

And what is remarkable, in order to knock out an electron in this way, one photon will be enough. With an increase in the light intensity, the number of photons (and hence the number of electrons knocked out) increases, but not the energy of a separately considered electron.

And this means that neither the energy nor the speed of the photoelectron in any way depend on the intensity of the light flux. The dependence is only on frequency.

As a result of such reasoning, the scientist derived the following formula:

This equation describes the energy of photoelectrons.

And it turns out that the photoelectric effect is nothing more than the phenomenon of the interaction of a light flux (or another electromagnetic radiation) with a material in which an electron is knocked out of an atom of a substance due to the exact hit of a quantum of light flow.

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