What is the chemical effect of light?

Today we will tell you what the chemical action of light is like, how this phenomenon is applied now and what is the history of its discovery.

Light and darkness

All literature (from the Bible to the modernfiction) exploits these two opposites. And always the light symbolizes a good start, and the dark - bad and evil. If you do not go into metaphysics and understand the essence of the phenomenon, then at the bottom of the eternal confrontation lies the fear of haze, or rather the lack of light.

Human eye and electromagnetic spectrum

The human eye is designed so that peopleperceive electromagnetic oscillations of a certain wavelength. The longest wavelength belongs to red light (λ = 380 nanometers), the shortest - to violet (λ = 780 nanometers). The full range of electromagnetic oscillations is much wider, and its visible part occupies only a tiny part. A person perceives infrared vibrations by another sense organ, the skin. People know this part of the spectrum as warm. Someone is able to see a bit of ultraviolet light (remember the main character of the film “Planet Ka-Pax”).

The main channel of receipt of information forhuman is the eye. Therefore, people lose the ability to assess what is happening around when visible light disappears after sunset. Dark forest becomes uncontrollable, dangerous. And where the danger is, there is the fear that someone unknown will come and “bite by the flank”. In the dark live terrible and evil creatures, and in the light - the good and understanding.

Electromagnetic wave scale. Part One: Low Energy

When the chemical action of light is considered, physics usually implies a visible spectrum.

In order to understand what is such a light, you must first talk about all possible variants of electromagnetic oscillation:

1. Radio waves.Their wavelength is so long that they can bend around the Earth. They are reflected from the ionic layer of the planet and carry information to people. Their frequency is 300 gigahertz or less, and the wavelength is from 1 millimeter or more (in the future - to infinity).
2. Infrared radiation.As we said above, a person perceives the infrared range as heat. The wavelength of this part of the spectrum is higher than that of the visible - from 1 millimeter to 780 nanometers, and the frequency is lower - from 300 to 429 terahertz.
3. Visible spectrum That part of the whole scale that the human eye perceives. Wavelength from 380 to 780 nanometers, frequency from 429 to 750 terahertz.

Electromagnetic wave scale. Part Two: High Energy

The waves listed further bear a double meaning: they are deadly for life, but at the same time, biological existence could not have arisen.

1. Ultraviolet radiation.The energy of these photons is higher than the visible. They are supplied by our central body, the Sun. And the characteristics of the radiation are: wavelength from 10 to 380 nanometers, frequency from 3 * 10¹⁴ up to 3 * 10¹⁶ Hertz.
2. X-rays.Everyone who broke bones is familiar with them. But these waves are applied not only in medicine. And they are emitted by electrons at a high speed, which slow down in a strong field, or by heavy atoms, from which an electron is pulled out from the inner shell. Wavelength from 5 picometers to 10 nanometers, frequency fluctuates between 3 * 10 values¹⁶-6 * 10¹⁹ Hertz.
3. Gamma radiation.The energy of these waves often coincides with the X-ray ones. Their spectrum overlaps significantly, only the source of origin varies. Gamma rays occur only during nuclear radioactive processes. But, unlike X-rays, γ-radiation can also have higher energies.

We led the main sections of the scaleelectromagnetic waves. Each of the ranges is divided into smaller sections. For example, one can often hear “hard x-rays” or “vacuum ultraviolet”. But this division itself is conditional: where the boundaries of one and the beginning of a different spectrum are rather difficult to determine.

Light and memory

Как мы уже говорили, основной поток информации the human brain gets through sight. But how to keep important points? Prior to the invention of photography (the chemical action of light involved in this process directly), one could write his impressions in a diary or invite the artist to write a portrait or a picture. The first method suffers from subjectivity, the second - not everyone can afford.

As always, chance has helped find an alternative to literature and painting. The ability of silver nitrate (AgNO₃) darken in the air has long been known.Based on this fact, a photo was built. The chemical action of light is that photon energy contributes to the release of pure silver from its salt. The reaction can not be called purely physical.

In 1725, the German physicist I. G. Schulz accidentally mixed nitric acid, in which silver was dissolved, with chalk. And then also accidentally noticed that the sunlight darkens the mixture.

Then followed a series of inventions. Photos were printed on copper, paper, glass, and, finally, on a polymer film.

Lebedev Experiments

Above we have told that practicalthe need to preserve images led to experimentation, and later to theoretical discoveries. Sometimes it happens the other way around: an already calculated fact needs to be confirmed by experiment. The fact that the photons of light are not only waves, but also particles, scientists have guessed for a long time.

Лебедев построил прибор, основанный на крутильных scales. When the light fell on the plate, the arrow deviated from the position "0". So it was proved that the photons transmit impulses to the surfaces, which means they put pressure on them. And the chemical action of light is directly related to this.

As Einstein has already shown, mass and energy aresame. Consequently, the photon, "dissolving" in the substance, gives it its essence. The body can use the received energy in different ways, including for chemical transformations.

Nobel Prize and Electrons

Albert Einstein, a scientist already mentioned by us, is known for his special theory of relativity, the formula E = mc² and evidence of relativistic effects.But he received the main prize of science not for this, but for another very interesting discovery. A series of experiments proved that light can "pull out" an electron from the surface of an illuminated body. This phenomenon is called an external photoelectric effect. A little later, the same Einstein discovered that there is an internal photoelectric effect: when an electron does not leave the body under the action of light, but is redistributed, it passes into the conduction band. And the lighted substance changes the conductivity property!

Areas in which this phenomenon appliesmany: from cathode lamps to "inclusion" in the network of semiconductors. Our life in its modern form would have been impossible without the use of a photoelectric effect. The chemical action of light only confirms that the photon energy in matter can be transformed into various forms.

Ozone holes and white spots

Slightly above, we said that when chemicalreactions occur under the action of electromagnetic radiation, implies the optical range. The example we want to give now stands out a little beyond this.

Recently, scientists around the planet were alarmed:An ozone hole is hanging over Antarctica, it is expanding all the time, and this is sure to end badly for the Earth. But then it turned out that all is not so scary. First, the ozone layer above the sixth continent is simply thinner than in other places. Secondly, fluctuations in the size of this spot do not depend on human activity, they are determined by the intensity of sunlight.

Но откуда вообще берется озон?And this is just a light-chemical reaction. The ultraviolet radiation that the sun radiates meets with oxygen in the upper atmosphere. There is a lot of ultraviolet radiation, little oxygen, and it is rarefied. Above only open space and vacuum. And the energy of ultraviolet radiation can break down the stable molecules.₂ on two atomic oxygen. And then the next UV quantum contributes to the creation of the compound O₃. This is ozone.

Ozone gas is deadly for all living things.It is very effective at killing bacteria and viruses that are used by humans. A small concentration of gas in the atmosphere is not harmful, but inhaling pure ozone is prohibited.

This gas also absorbs very efficiently.ultraviolet quanta. Therefore, the ozone layer is so important: it protects the inhabitants of the surface of the planet from an overabundance of radiation that can sterilize or kill all biological organisms. We hope, now it is clear, in what the chemical action of light is manifested.