Quantum physics: quantum properties of light

Have you ever thought about what many light phenomena really are? For example, let's take a photoelectric effect, thermal waves, photochemical processes and the like - all these are quantum properties of light. If they had not been discovered, the works of scientists would not have moved from a dead center, in fact, like scientific and technological progress. They study them in the section of quantum optics, which is inextricably linked with the same section of physics.

Quantum properties of light: definition of the term

Until recently, a clear and understandable interpretation of this optical phenomenon could not be given. They were successfully used in science and everyday life, on its basis they built not only formulas, but also whole problems in physics. Formulate the final definition was obtained only from modern scientists who summed up the work of their predecessors. So, the wave and quantum properties of light are a consequence of the peculiarities of its radiators, which are the electrons of atoms. The quantum (or photon) is formed due to the fact that the electron passes to a lower energy level, thereby generating electro-magnetic pulses.

The first optical observations

XIX столетии. The assumption that light has quantum properties appeared in the XIX century. Scientists discovered and diligently studied such phenomena as diffraction, interference and polarization. With their help, the electromagnetic wave theory of light was derived. It was based on the acceleration of the motion of electrons during the oscillation of the body. Due to this, heating occurred, followed by light waves. The first author's hypothesis on this account was formed by the Englishman D. Rayleigh. He regarded radiation as a system of identical and constant waves, and in a closed space. According to his conclusions, with decreasing wavelength, their power should continuously increase, moreover, ultraviolet and X-ray waves were required. In practice, all this was not confirmed, and another theoretician took up the work.

Planck's formula

XX века Макс Планк – физик немецкого происхождения – выдвинул интересную гипотезу. At the very beginning of the 20th century, Max Planck - a physicist of German descent - advanced an interesting hypothesis. According to her, the radiation and absorption of light does not proceed continuously, as previously thought, but in batches - by quanta, or, as they are also called, photons. h , и он был равен 6,63·10 ^-34 Дж·с. Planck's constant - proportionality coefficient, designated by the letter h was introduced , and it was equal to 6.63 · 10 ^{-34 Js} . v – частота света. In order to calculate the energy of each photon, one more quantity was required - v - the frequency of light. The Planck constant was multiplied by the frequency, and as a result, the energy of a single photon was obtained. So the German scientist accurately and correctly fixed in a simple formula the quantum properties of light, which were previously discovered by H. Hertz and designated by him as a photoelectric effect.

Opening the photoelectric effect

As we have already said, the scientist Heinrich Hertz was the first to pay attention to the quantum properties of light that were not previously noted. The photoelectric effect was discovered in 1887, when the scientist connected the illuminated zinc plate and the rod of the electrometer. In the event that a positive charge reaches the plate, the electrometer is not discharged. If the charge is emitted negative, the device starts discharging as soon as the ultraviolet ray hits the plate. In the course of this practical experience it was proved that the plate under the influence of light can emit negative electric charges, which subsequently received the corresponding name - electrons.

Practical experiments Stoletova

Practical experiments with electrons were conducted by the Russian researcher Alexander Stoletov. For his experiments, he used a vacuum glass bottle and two electrodes. One electrode was used to transmit energy, and the second was illuminated, and a negative pole of the battery was applied to it. During this operation, the current strength began to increase, but after a while it became constant and directly proportional to the radiation of the light flux. As a result, it was revealed that the kinetic energy, as well as the retarding electron voltages, do not depend on the power of the light radiation. But the increase in the frequency of light makes this figure grow.

New quantum properties of light: the photoelectric effect and its laws

In the course of the development of Hertz's theory and Stoletov's practice, three basic laws were derived, according to which, as it turned out, photons function:

Мощность светового излучения, которое падает на поверхность тела, прямо пропорциональна силе тока насыщения. 1. The power of the light radiation, which falls on the surface of the body, is directly proportional to the saturation current.

Мощность светового излучения никак не влияет кинетическую энергию фотоэлектронов, а вот частота света является причиной линейного роста последней. 2. The power of light radiation does not affect the kinetic energy of the photoelectrons, but the frequency of light is the cause of the linear growth of the latter.

Существует некая «красная граница фотоэффекта». 3. There is a certain "red border of the photoeffect". The bottom line is that if the frequency is less than the minimum frequency of light for a given substance, then the photoelectric effect is not observed.

Difficulties in collision of two theories

After the formula developed by Max Planck, science ran into a dilemma. Previously derived wave and quantum properties of light, which were discovered later, could not exist within the framework of generally accepted physical laws. In accordance with the electromagnetic, old theory, all the electrons of the body, on which light enters, must come into forced oscillation at equal frequencies. This would generate infinitely large kinetic energy, which is impossible. Moreover, to accumulate the necessary amount of energy, the electrons needed to remain at rest for dozens of minutes, while the phenomenon of the photoelectric effect is observed in practice without the slightest delay. Additional confusion arose also because the energy of the photoelectrons did not depend on the power of the light radiation. In addition, the red boundary of the photoelectric effect has not yet been discovered, nor has the proportionality of the electron light kinetic energy frequency been calculated. The old theory could not clearly explain the physical phenomena visible to the eye, and the new one was not yet fully worked out.

Rationalism of Albert Einstein

Only in 1905 the brilliant physicist A. Einstein revealed in practice and clearly formulated in theory what it is - the true nature of light. Wave and quantum properties, discovered with the help of two opposing hypotheses, are inherent in photons in equal parts. For completeness, the picture lacked only the principle of discreteness, that is, the exact location of quanta in space. Each quantum is a particle that can be absorbed or radiated as a whole. An electron, "swallowing" a photon inside itself, increases its charge by the value of the energy of the absorbed particle. Further, inside the photocathode the electron moves to its surface, while retaining a "double portion" of energy, which at the output turns into kinetic. In such a simple way, a photoelectric effect is realized, in which there is no delayed reaction. At the finish, the electron releases a quantum of itself, which falls to the surface of the body, radiating even more energy. The more the number of released photons - the more powerful the radiation, respectively, and the oscillation of the light wave increases.

The simplest devices, based on the principle of the photoelectric effect

After the discoveries made by German scientists at the dawn of the twentieth century, the active application of the quantum properties of light for the manufacture of various instruments began. Inventions, the principle of action of which lies in the photoelectric effect, is called photocells, the simplest representative of which is the vacuum one. Among its shortcomings can be called weak current conductivity, low sensitivity to radiation of long waves, because of what it can not be used in alternating current circuits. The vacuum device is widely used in photometry, it measures the brightness and quality of light. It also plays an important role in photophone and in the process of sound reproduction.

Photocells with conductor functions

This is a completely different type of devices, based on the quantum properties of light. Their purpose is to change the concentration of current carriers. This phenomenon is sometimes called an internal photoelectric effect, and it forms the basis of photoresistors. These semiconductors play a very important role in our daily lives. They were first used in retro cars. Then they provided the work of electronics and batteries. In the middle of the twentieth century, such photocells began to be used for the construction of spacecraft. Until now, due to the internal photoelectric effect turnstiles in the metro, portable calculators and solar panels.

Photochemical reactions

Light, whose nature was only partially available to science in the twentieth century, in fact affects the chemical and biological processes. Under the influence of quantum flows, the process of dissociation of molecules begins and their merging with atoms. In science, this phenomenon is called photochemistry, and in nature, one of its manifestations is photosynthesis. It is due to light waves in the cells that processes are carried out for the release of certain substances into the intercellular space, due to which the plant acquires a green tint.

The quantum properties of light also affect human vision. Getting on the retina of the eye, the photon provokes the decomposition of the protein molecule. This information is transported through neurons to the brain, and after its processing we can see everything under light. With the onset of darkness, the protein molecule is restored, and vision is accomodated to new conditions.

Results

In the course of this article, we found out that mainly the quantum properties of light are manifested in a phenomenon called the photoelectric effect. Each photon has its own charge and mass, and collides with an electron inside it. Quantum and electron become one, and their joint energy turns into kinetic, which, strictly speaking, is required for the realization of the photoelectric effect. Wave oscillations can increase the energy produced by the photon, but only up to a certain value.

The photoelectric effect is an indispensable component of most types of technology these days. It is based on space liners and satellites, develops solar batteries, and is used as a source of auxiliary energy. In addition, light waves have a huge impact on the chemical-biological processes on Earth. Due to simple sunlight, the plants become green, the earth's atmosphere is painted in the entire palette of blue, and we see the world as it is.