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 science 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 fear of the mist, or rather, the absence of light, lies at the foundation of the eternal confrontation.
The human eye and electromagnetic spectrum
The human eye is designed so that people perceive electromagnetic waves of a certain wavelength. The longest wavelength belongs to red light (λ = 380 nanometers), the shortest - to 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 by another sensory organ - the skin. People know this part of the spectrum as warm. Someone is able to see a little ultraviolet (remember the main character of the film "Planet Ka-Pax").
The main channel of information for a person is the eye. Therefore, people lose their ability to evaluate what is happening around when, after sunset, visible light disappears. The dark forest becomes unmanageable, dangerous. And where there is danger, there is fear that someone unknown will come and “bite by the barrel”. Scary and evil creatures live in the dark, and good and understanding in the light.
Scale of electromagnetic waves. Part One: Low Energy
When considering the chemical effect of light, physics implies a usually visible spectrum.
In order to understand what light is in general, you should first talk about all the possible options for electromagnetic oscillation:
- Radio waves. Their wavelength is so great 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 is 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 in this part of the spectrum is higher than in the visible one - from 1 millimeter to 780 nanometers, and the frequency below - from 300 to 429 terahertz.
- Visible spectrum. That part of the whole scale that the human eye perceives. The wavelength is from 380 to 780 nanometers, the frequency is from 429 to 750 terahertz.
Scale of electromagnetic waves. Part Two: High Energies
The waves listed below have a double meaning: they are mortally dangerous for life, but at the same time, biological existence could not have arisen without them.
- Ultraviolet radiation. The energy of these photons is higher than visible. They are supplied by our central luminary, the Sun. And the characteristics of radiation are as follows: wavelength from 10 to 380 nanometers, frequency from 3 * 10 14 to 3 * 10 16 Hertz.
- X-rays. Everyone who broke bones is familiar with them. But these waves are used not only in medicine. And their electrons emit at a high speed, which slows down in a strong field, or heavy atoms, from which an electron was pulled out of the inner shell. The wavelength is from 5 picometers to 10 nanometers, the frequency varies between 3 * 10 16 -6 * 10 19 Hertz.
- Gamma radiation. The energy of these waves often coincides with the x-ray. Their spectrum overlaps significantly, only the source of origin is different. Gamma rays occur only in nuclear radioactive processes. But, unlike x-rays, γ-radiation is able to have higher energies.
We have given the main sections of the electromagnetic wave scale. Each of the ranges is divided into smaller sections. For example, you can often hear "hard X-rays" or "vacuum ultraviolet." But this division itself is conditional: where the boundaries of one and the beginning of another spectrum are difficult to determine.
Light and memory
As we have already said, the human brain receives the main stream of information through vision. But how to save important points? Before the invention of photography (the chemical action of light is directly involved in this process), one could write down his 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.
As always, an opportunity helped to find an alternative to literature and painting. The ability of silver nitrate (AgNO 3 ) to darken in air has long been known. Based on this fact, a photograph was built. The chemical effect of light lies in the fact that the energy of a photon promotes the release of pure silver from its salt. The reaction cannot 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 he also accidentally noticed that sunlight obscures the mixture.
Then a series of inventions followed. Photographs were printed on copper, paper, glass, and, finally, on a polymer 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. Scientists have guessed for a long time that photons of light are not only waves, but also particles.
Lebedev built a device based on torsion scales. 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 is directly related to this.
As Einstein has already shown, mass and energy are one and the same. Consequently, a photon, "dissolved" in matter, gives it its essence. The body can use the received energy in different ways, including for chemical transformations.
Nobel Prize and Electrons
The already mentioned scientist Albert Einstein is known for his special theory of relativity, the formula E = mc 2, and the proof of relativistic effects. But he did not receive the main science prize for this, but for another very interesting discovery. Einstein proved by several experiments that light can “tear” an electron from the surface of an illuminated body. This phenomenon is called an external photoelectric effect. And a little later, the same Einstein discovered that there is an internal photoelectric effect: when an electron does not leave the body under the influence of light, but redistributes, it passes into the conduction band. And the lit substance changes the property of conductivity!
There are many areas in which this phenomenon is applied: from cathode lamps to “inclusion” in a semiconductor network. Our life in its modern form would be impossible without the use of the photoelectric effect. The chemical action of light only confirms that the photon energy in a substance can be converted into various forms.
Ozone holes and white spots
We said a little higher that when chemical reactions occur under the influence of electromagnetic radiation, the optical range is implied. The example we want to give now is a little beyond this framework.
Recently, scientists around the planet have sounded the alarm: an ozone hole hangs over Antarctica, it expands all the time, and this will certainly end badly for the Earth. But then it turned out that everything was not so scary. Firstly, the ozone layer over the sixth continent is simply thinner than in other places. Secondly, fluctuations in the size of this spot are not dependent on human activity, they are determined by the intensity of sunlight.
But where does ozone come from? And this is just a light-chemical reaction. The ultraviolet radiation that emits from the sun is found with oxygen in the upper atmosphere. There is a lot of ultraviolet, little oxygen, and it is rarefied. Above is just outer space and vacuum. And the energy of ultraviolet radiation is capable of breaking stable O 2 molecules into two atomic oxygen. And then the next UV quantum contributes to the creation of compounds About 3 . This is ozone.
Gas ozone is deadly for all living things. It very effectively kills 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.
And also this gas absorbs ultraviolet quanta very efficiently. 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 it is now clear how the chemical action of light is manifested.