The chemical action of light in what appears?

Today we will tell you what is the chemical action of light, as it is used now and what is the history of its discovery.

Light and dark

All the literature (from the Bible to modern fiction) exploits these two opposites. And always the light symbolizes a good beginning and dark – bad and evil. If you do not go into metaphysics to understand the nature of phenomena, the basis of the eternal conflict lies fear of darkness, or rather, the lack of light.

Human eyes and the electromagnetic spectrum

The Human eye is designed so that people perceive electromagnetic waves of a certain wavelength. The largest wavelength belongs to red light (λ=380 nanometers), the shortest-purple (λ=780 nanometers). Full spectrum of electromagnetic waves is much broader and the visible part is only a tiny part. Infrared vibrations of a person perceives another sensory organ - the skin. This part of the spectrum people know as heat. Someone capable of seeing some UV light (remember the main character of the film «K-pax").

The Main channel for receiving information for a person – the eye. Therefore, people lose the ability to assess what is happening around, after sunset, when the visible light disappears. The dark forest becomes uncontrollable, dangerous. But where danger is, there is fear that there will be someone unknown and “bite for a flank”. Live in the dark scary and evil creatures, and at every turn – kind and understanding.

The Scale of electromagnetic waves. Part one: low energy

When one considers the chemical action of light, physics usually involves the visible spectrum.

In order to understand what a light, you should first tell about all the possible options electromagnetic waves:

1. Radio waves. The wavelength is so large that they can envelop the Earth. They bounce off the ionic layer of the planet and carry information to people. The frequency equal to 300 GHz and less, and the wavelength – 1 mm or more (in the future – to infinity).
2. Infrared light. As we have said above, people perceive the IR range as heat. The wavelength in this part of the spectrum higher than the visible – from 1 mm to 780 nm, and the frequency is below – from 300 to 429 terahertz.
3. The Visible spectrum. The part of the entire scale that the human eye can apprehend. Wavelength from 380 to 780 nanometers, frequency from 429 to 750 terahertz.

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The Scale of electromagnetic waves. Part two: high energy

On These waves carry a double meaning: they are deadly to life, but at the same time without their biological existence could not arise.

1. Ultraviolet radiation. The energy of these photons higher than visible. Their supplies our Central luminary, the Sun. And the characteristics of the radiation are: wavelength of 10 to 380 nanometers, a frequency of 3 × 10¹⁴ to 3*10¹⁶ Hz.
2. X-rays. Everyone is familiar with them, who broke bones. But these waves are used not only in medicine. And emit their electrons with a high velocity that impede in a strong field, or with heavy atoms, which threw up an electron from the inner shell. Wavelength from 5 PM to 10 nanometers, frequency ranging between the values of 3*10¹⁶-6*10¹⁹ Hz.
3. Gamma rays. The energy of these waves often coincides with the x-ray. Their range significantly overlaps, it differs only in the source of origin. Gamma-rays are produced only in nuclear radioactive processes. But, unlike x-rays, γ-rays are able to have higher energy.

We brought the main sections of the scale of electromagnetic waves. Each range is divided into smaller sections. For example, you can often hear “hard x-rays” or “vacuum UV”. But this separation is conditional: where the boundaries of one and the beginning of another spectrum is difficult to determine.

Light and memory

As we have said, the main flow of information the human brain receives through vision. But how to preserve important moments? Before the invention of photography (the chemical action of light involved in this process directly) their experiences can be written in the diary or call the artist that he painted a portrait or picture. The first method suffers from subjectivity, the second – not everyone can afford.

As always, to find an alternative to the literature and painting came about by accident. The ability of silver nitrate (AgNO₃) to darken in the air has long been known. On the basis of this fact was built photo. The chemical action of light is that the photon energy contributes to the isolation of the pure silver from its salts. The reaction can not be called purely physical.

In 1725, the German physicist I. G. Schultz accidentally mixed nitric acid, which was dissolved in silver chalk. And then also happened to notice that the sunlight darkens the mixture.

Then came a number of inventions. The photos were printed on copper, paper, glass, and finally plastic wrap.

Experiments Lebedev

Above we said that a practical need to preservethe images led to experimentation, and further – theoretical discoveries. Sometimes Vice versa: already calculated fact required to confirm the experiment. That the photons of light – it's not just waves, but particles, scientists knew for a long time.

Lebedev built a device based on torsion balances. When the plates catches the light, the arrow has deviated from the provisions of the “0”. It was proved that the photons transfer momentum to the surfaces, and therefore, exert pressure on them. And the chemical action of light has a lot to do with it.

As already shown by Einstein, mass and energy-are one and the same. Consequently, photon, "dissolving" the substance that gives it its essence. Received energy the body can use in different ways, including for chemical transformations.

The Nobel prize and electrons

Already mentioned by us scientist albert Einstein is famous due to the special theory of relativity, the formula E=mc² and the proof of relativistic effects. But he got the main prize of science is not for it, and for another very interesting discovery. Einstein a number of experiments proved that light can “snatch” from the surface of the illuminated body electron. This phenomenon is called external photoelectric effect. A little later the same Einstein discovered that there is an internal photoelectric effect: when an electron under the action of light does not leave the body, and redistributed, transferred into the conduction band. And lighted the substance changes the conductivity property!

Areas that use this phenomenon are numerous: from cathode lamps to “enable” the network of semiconductors. Our life in its modern form would not have been possible without the use of the photoelectric effect. The chemical action of light only confirms the fact that the photon energy in a substance can be converted into various forms.

Ozone holes and white spots

Just above we said that when chemical reactions occur under the action of electromagnetic radiation, means an optical range. An example that we want to bring now is a little beyond that.

Recently, scientists of the entire planet sounded the alarm over the looming Antarctic ozone hole, it bends, and it is sure to end badly for the Earth. But then it turned out that all not so scary. First, the ozone layer over the sixth continent is just more subtle than in other places. Second, fluctuations in the size of the spots does not depend on human activity, determines the sunlight intensity.

But where do does the ozone? And this is just a light-chemical reaction. Ultraviolet light, which radiates the Sun meets oxygen in the upper atmosphere. A lot of ultraviolet light, little oxygen, and he is thin. The above is just the open space and the vacuum. And energy UV radiation is able to break up stable molecules O₂ into two atomic oxygen. And then following UV quantum helps create connections On₃. This is ozone.

Ozone is a Gas deadly to all living things. It very effectively kills bacteria and viruses that are used by man. A small gas concentration in the atmosphere is not harmful, but inhaling pure ozone is prohibited.

And yet this gas is very effective in absorbing ultraviolet rays. Therefore, the ozone layer is so important: it protects the inhabitants of the planet's surface from excess radiation, which is able to sterilize or kill all biological organisms. I hope now it is clear what is the chemical action of light.