Today we will tell you what the chemical effect of light is, how this phenomenon is applied now and what is the history of its discovery.
Light and darkness
All literature (from the Bible to modern fiction) exploits these two opposites. Moreover, light always symbolizes a good beginning, and darkness - bad and evil. If you do not go into metaphysics and understand the essence of the phenomenon, then the basis of the eternal confrontation is the fear of darkness, or rather, the absence of light.
The human eye and the electromagnetic spectrum
The human eye is designed so that people perceive electromagnetic vibrations of a certain wavelength. The longest wavelength belongs to red light (λ=380 nanometers), the shortest - violet (λ=780 nanometers). The full spectrum of electromagnetic oscillations is much wider, and its visible part occupies only a tiny part. A person perceives infrared vibrations with another sense organ - the skin. This part of the spectrum people know as heat. Someone is able to see a little ultraviolet (think of the main character in the movie "Planet Ka-Pax").
Main channelinformation for a person is the eye. Therefore, people lose the ability to assess what is happening around when visible light disappears after sunset. The dark forest becomes uncontrollable, dangerous. And where there is danger, there is also the fear that someone unknown will come and "bite the barrel." Scary and evil creatures live in the dark, but kind and understanding creatures live in the light.
Scale of electromagnetic waves. Part One: Low Energies
When considering the chemical action of light, physics means the normally visible spectrum.
In order to understand what light is in general, you should first talk about all the possible options for electromagnetic oscillations:
- Radio waves. Their wavelength is so long that they can go 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 - from 1 millimeter or more (in the future - to infinity).
- 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.
- 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.
Scale of electromagnetic waves. Part Two: High Energies
The waves listed below have a double meaning: they are deadlydangerous to life, but at the same time, without them, biological existence could not have arisen.
- UV radiation. The energy of these photons is higher than that of visible ones. They are supplied by our central luminary, the Sun. And the characteristics of the radiation are as follows: wavelength from 10 to 380 nanometers, frequency from 31014 to 31016 Hertz.
- X-rays. Anyone who has broken bones is familiar with them. But these waves are used not only in medicine. And their electrons radiate at high speed, which slows down in a strong field, or heavy atoms, in which an electron was pulled out from the inner shell. Wavelength from 5 picometers to 10 nanometers, frequency ranges between 31016-61019 Hertz.
- Gamma radiation. The energy of these waves often coincides with that of X-rays. Their spectrum overlaps significantly, only the source of origin differs. Gamma rays are produced only by nuclear radioactive processes. But, unlike X-rays, γ-radiation is capable of higher energies.
We have given the main sections of the scale of electromagnetic waves. Each of the ranges is divided into smaller sections. For example, "hard x-rays" or "vacuum ultraviolet" can often be heard. But this division itself is conditional: it is rather difficult to determine where the boundaries of one and the beginning of another spectrum are.
Light and memory
As we have already said, the human brain receives the main flow of information through vision. But how do you save important moments? Before the invention of photography (the chemical action of light is involved in thisprocess directly), one could write down one's impressions in a diary or call an artist to paint a portrait or a picture. The first way sins subjectivity, the second - not everyone can afford it.
As always, chance helped to find an alternative to literature and painting. The ability of silver nitrate (AgNO3) to darken in air has long been known. Based on this fact, a photograph was built. The chemical effect of light is that the photon energy contributes to the separation of pure silver from its s alt. The reaction is by no means purely physical.
In 1725, the German physicist I. G. Schultz accidentally mixed nitric acid, in which silver was dissolved, with chalk. And then I also accidentally noticed that the sunlight darkens the mixture.
A number of inventions followed. Photos were printed on copper, paper, glass, and finally on plastic film.
Lebedev's experiments
We said above that the practical need to save images led to experiments, 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 photons of light are not only waves, but also particles, scientists have long guessed.
Lebedev built a device based on torsion balances. When light fell on the plates, the arrow deviated from the "0" position. So it was proved that photons transmit momentum to surfaces, which means that they exert pressure on them. And the chemical action of light has a lot to do with it.
As Einstein already showed, mass and energy are one and the same. 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
Already mentioned scientist Albert Einstein is known for his special theory of relativity, formula E=mc2 and proof of relativistic effects. But he received the main prize of science not for this, but for another very interesting discovery. Einstein proved in a series of experiments that light can "pull out" an electron from the surface of an illuminated body. This phenomenon is called the external photoelectric effect. A little later, the same Einstein discovered that there is also an internal photoelectric effect: when an electron under the influence of light does not leave the body, but is redistributed, it passes into the conduction band. And the illuminated substance changes the property of conductivity!
Fields in which this phenomenon is applied are many: from cathode lamps to "inclusion" in the semiconductor network. Our life in its modern form would be impossible without the use of the photoelectric effect. The chemical effect of light only confirms that the energy of a photon in matter can be converted into various forms.
Ozone holes and white spots
A little higher we said that when chemical reactions occur under the influence of electromagnetic radiation, the optical range is implied. The example we want to give now goes a little beyond that.
Recently, scientists around the world sounded the alarm: over Antarcticathe ozone hole is hanging, it is expanding all the time, and this will definitely end badly for the Earth. But then it turned out that everything is not so scary. First, the ozone layer over the sixth continent is simply thinner than elsewhere. Secondly, fluctuations in the size of this spot do not depend on human activity, they are determined by the intensity of sunlight.
But where does ozone even come from? And this is just a light-chemical reaction. The ultraviolet that the sun emits meets oxygen in the upper atmosphere. There is a lot of ultraviolet, little oxygen, and it is rarefied. Above only open space and vacuum. And the energy of ultraviolet radiation is capable of breaking the stable O2 molecules into two atomic oxygens. And then the next UV quantum contributes to the creation of the O3 connection. This is ozone.
Ozone gas is deadly to all living things. It is very effective in killing bacteria and viruses that are used by humans. A small concentration of gas in the atmosphere is not harmful, but it is forbidden to inhale pure ozone.
And this gas very effectively absorbs ultraviolet quanta. Therefore, the ozone layer is so important: it protects the inhabitants of the planet's surface from an excess of radiation that can sterilize or kill all biological organisms. We hope that now it is clear what the chemical effect of light is.
