The range of frequencies emitted by electromagnetic waves is huge. It is determined by all possible frequencies of oscillations of charged particles. Such fluctuations occur with alternating current in power lines, antennas of radio and television stations, mobile phones, radars, lasers, incandescent and fluorescent lamps, radioactive elements, x-ray machines. The frequency range of electromagnetic waves recorded at the present time extends from 0 to 3*10 22 Hz. This range corresponds to the spectrum (from Latin spectrum vision, image) of electromagnetic waves with a wavelength λ varying from 10 - 14 m to infinity. Wavelength λ= c/ν, where c=3*10 8 m/s is the speed of light, and ν is the frequency. On fig. 1.1 shows the considered spectrum of electromagnetic waves.
Rice. 1.1 Spectrum of electromagnetic radiation
Radio waves of different frequencies propagate differently within the Earth and in outer space and, therefore, find various applications in radio communications and in scientific research. Taking into account the characteristics of propagation, generation, it is customary to divide the entire range of radio waves by wavelength (or frequency) conditionally into twelve ranges. The division of radio waves into ranges in radio communications is established by the international radio regulations. Each range corresponds to a frequency band from 0.3*10 N to 3*10 N , where N is the range number. In a given frequency range N, only a finite number of radio stations that do not interfere with each other can be located. This number, called channel capacity, is defined as:
m=(3*10N - 0.3*10N)/Δf
where Δf is the frequency band of the radio signal.
Let the bandwidth of the analog television signal (TV) be 8 MHz, taking into account the guard gaps, we will take Δf=10 MHz, then in the meter band (N=8) the number of TV channels will be 27. Under the same conditions in the decimeter band, the number of channels will increase to 270. This is one of the main reasons for the desire to master ever higher frequencies. Examples of dividing the most used ranges and areas of their use are shown in Table 1.1.
| N | Designation | Bandwidth | Wave length, m | Range name | Application area |
| 4 | VLF Very low frequencies | 3…30 kHz | 10 5 …10 4 | Meriametric | Communication around the world and over long distances. Radio navigation. Underwater communications |
| 5 | LF Low frequencies | 30…300 kHz | 10 4 …10 3 | Kilometer | Long distance communications, frequency and time reference stations, longwave broadcasts |
| 6 | MF Mid frequencies | 300…3000 kHz | 10 3 …10 2 | Hectameter | Medium-wave local and regional broadcasting. ship communications |
| 7 | HF High frequencies | 3…30 MHz | 100…10 | Decameter | Communication over long distances and shortwave broadcasting |
| 8 | VHF Very high frequencies | 30…300 MHz | 10…1 | Meter | Communication within line of sight. Mobile connection. TV and FM broadcasting. RRL |
| 9 | UHF ultra high frequencies | 300…3000 MHz | 1…0,1 | decimeter | VHF. Communication within the line of sight and mobile communications. TV broadcast. RRL |
| 10 | microwave Ultra high frequencies | 3…30 GHz | 0,1…0,01 | centimeter | VHF. RRL. Radar. Satellite communication systems |
| 11 | EHF Extreme high frequencies | 30…300 GHz | 0,01…0,001 | millimeter | VHF. Inter-satellite communications and microcellular radiotelephone communications |
Let us briefly characterize the boundaries of the ranges of wavelengths (frequencies) in the spectrum of electromagnetic waves in order of increasing radiation frequency, and also indicate the main sources of radiation in the corresponding range.
Sound frequency waves occur in the frequency range from 0 to 2*10 4 Hz (λ = 1.5*10 4 ÷ ∞ m). The source of sound frequency waves is an alternating current of the corresponding frequency. Given that the intensity of electromagnetic wave radiation is proportional to the fourth power of frequency, the radiation of such relatively low frequencies can be neglected. It is for this reason that the 50 Hz AC line emission can often be neglected.
Radio waves occupy the frequency range 2*10 4 - 10 9 Hz (λ = 0.3 - 1.5*10 4 m). The source of radio waves, as well as waves of sound frequencies, is alternating current. However, the high frequency of radio waves in comparison with the waves of sound frequencies leads to a noticeable radiation of radio waves into the surrounding space. This allows them to be used to transmit information over a considerable distance (broadcasting, television (TV)), radar, radio navigation, radio control systems, radio relay lines (RRL), cellular communication systems, professional mobile communication systems - trunking systems, mobile satellite communication systems, wireless telephone communication systems (radio extenders), etc.
Microwave radiation, or microwave radiation, occurs in the frequency range 10 9 - 3 * 10 n Hz (λ = 1 mm - 0.3 m). The source of microwave radiation is a change in the direction of the spin of the valence electron of an atom or the speed of rotation of the molecules of a substance. Given the transparency of the atmosphere in this range, microwave radiation is used for space communications. In addition, this radiation is used in household microwave ovens.
Infrared (IR) radiation occupies the frequency range 3*10 11 - 3.85*10 14 Hz (λ = 780 nm - 1 mm). IR radiation was discovered in 1800 by the English astronomer William Herschel. Studying the rise in temperature of a thermometer heated by visible light, Herschel found the greatest heating of the thermometer outside the visible light region (beyond the red region). Invisible radiation, given its place in the spectrum, was called infrared.
The source of infrared radiation is the vibration and rotation of the molecules of matter, therefore, IR electromagnetic waves radiate heated bodies, the molecules of which move especially intensively. IR radiation is often referred to as thermal radiation. About 50% of the Sun's energy is emitted in the infrared. The maximum radiation intensity of the human body falls on a wavelength of 10 microns. The dependence of the intensity of IR radiation on temperature makes it possible to measure the temperature of various objects, which is used in night vision devices, as well as when detecting foreign formations in medicine. Remote control of the TV and VCR is carried out using infrared radiation.
This range is used to transmit information over optical quartz fibers. Let us estimate, as for radio waves, the width of the optical range.
Let the optical range change from λ1 = 1200 nm to λ2=1620 nm. Knowing the value of the speed of light in vacuum c \u003d 2.997 * 10 8 m / s, (rounded 3 * 10 8 m / s) from the formula f=c/λ, for λ1 and λ2 we obtain f1 = 250 THz and f2 = 185 THz, respectively. Therefore, the interval between frequencies ΔF = f1 - f2 = 65 THz. For comparison: the entire frequency range from the audio range to the upper frequency of the microwave range is only 30 GHz, and ultra microwave is 300 GHz, i.e. 2000 - 200 times smaller than the optical one.
Visible light is the only range of electromagnetic waves perceived by the human eye. Light waves occupy a fairly narrow range: 380-780 nm (λ = 3.85 * 10 14 - 7.89 * 10 14 Hz).
The source of visible light is valence electrons in atoms and molecules that change their position in space, as well as free charges moving at an accelerated rate. This part of the spectrum gives a person maximum information about the world around him. In terms of its physical properties, it is similar to other ranges of the spectrum, being only a small part of the spectrum of electromagnetic waves. The maximum sensitivity of the human eye falls on the wavelength λ= 560 nm. This wavelength also accounts for the maximum intensity of solar radiation and at the same time the maximum transparency of the Earth's atmosphere.
For the first time, an artificial light source was received by the Russian scientist A.N. Lodygin in 1872, passing an electric current through a carbon rod placed in a closed vessel from which air was pumped out, and in 1879 the American inventor T.A. Edison created a fairly durable and convenient incandescent lamp design.
There are a number of types of electromagnetic radiation, ranging from radio waves to gamma rays. Electromagnetic rays of all types propagate in a vacuum at the speed of light and differ from each other only in their wavelengths.
1859 spectroscopy
1864 Maxwell's equations
1864 SPECTRUM
ELECTROMAGNETIC RADIATION
1900 radiation
black body
After the advent of Maxwell's equations, it became clear that they predict the existence of a natural phenomenon unknown to science - transverse electromagnetic waves, which are oscillations of interconnected electric and magnetic fields propagating in space at the speed of light. James Clark Maxwell himself was the first to point out to the scientific community this consequence from the system of equations he derived. In this refraction, the speed of propagation of electromagnetic waves in vacuum turned out to be such an important and fundamental universal constant that it was designated by a separate letter c, in contrast to all other speeds, which are usually denoted by the letter v.
Having made this discovery, Maxwell immediately determined that visible light is "only" a variety of electromagnetic waves. By that time, the wavelengths of light in the visible part of the spectrum were known - from 400 nm (violet rays) to 800 nm (red rays). (A nanometer is a unit of length equal to one billionth of a meter, which is mainly used in atomic and ray physics; 1 nm = 10 -9 m.) All the colors of the rainbow correspond to different wavelengths that lie within these very narrow limits. However, Maxwell's equations contained no restrictions on the possible range of electromagnetic wavelengths. When it became clear that electromagnetic waves of very different lengths must exist, in fact, a comparison was immediately put forward about the fact that the human eye distinguishes such a narrow band of their lengths and frequencies: a person was likened to a listener of a symphony concert, whose hearing is capable of picking up only a violin part, not distinguishing all other sounds.
Shortly after Maxwell's prediction of the existence of electromagnetic waves in other ranges of the spectrum, a series of discoveries followed, confirming his correctness. Radio waves were the first to be discovered in 1888 by the German physicist Heinrich Hertz (1857-1894). The only difference between radio waves and light is that radio waves can range in length from a few decimeters to thousands of kilometers. According to Maxwell's theory, the cause of electromagnetic waves is the accelerated movement of electric charges. Oscillations of electrons under the influence of an alternating electrical voltage in the antenna of a radio transmitter create electromagnetic waves propagating in the earth's atmosphere. All other types of electromagnetic waves also arise as a result of various types of accelerated movement of electric charges.
Like light waves, radio waves can travel long distances through the earth's atmosphere with virtually no loss, making them the most useful carriers of coded information. Already at the beginning of 1894 - just over five years after the discovery of radio waves - the Italian physicist Gul-elmo Marconi (1874-1937) designed
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Electromagnetic waves form a continuous spectrum of wavelengths and energies (frequencies), subdivided into conditional ranges - from radio waves to gamma rays
the first working wireless telegraph - the prototype of modern radio - for which he was awarded the Nobel Prize in 1909.
After the existence of electromagnetic waves outside the visible spectrum, predicted by Maxwell's equations, was first experimentally confirmed, the remaining niches of the spectrum were filled very quickly. Today, electromagnetic waves of all ranges without exception are discovered, and almost all of them find wide and useful application in science and technology. The frequencies of the waves and the energies of the corresponding quanta of electromagnetic radiation (see bar constant) increase with decreasing wavelength. The totality of all electromagnetic waves forms the so-called continuous spectrum of electromagnetic radiation. It is subdivided into the following ranges (in order of increasing frequency and decreasing wavelength):
radio waves
As already noted, radio waves can vary significantly in length - from a few centimeters to hundreds and even thousands of kilometers, which is comparable to the radius of the globe (about 6400 km). Waves of all radio bands are widely used in technology - decimeter and ultrashort meter waves are used for television and radio broadcasting in the frequency modulated ultrashort waves (VHF / BYU), providing high quality signal reception within the zone of direct wave propagation. Radio waves of the meter and kilometer range are used for broadcasting and radio communication over long distances using amplitude modulation (AM), which, although at the expense of signal quality, ensures its transmission over arbitrarily long distances within the Earth due to the reflection of waves from the planet's ionosphere. However, today this type of communication is becoming a thing of the past due to the development of satellite communications. Waves of the decimeter range cannot go around the earth's horizon like meter waves, which limits the reception area to a direct propagation area, which, depending on the antenna height and transmitter power, ranges from several to several tens of kilometers. And here satellite repeaters come to the rescue, taking on the role of radio wave reflectors, which the ionosphere plays in relation to meter waves.
Microwave
Microwaves and radio waves in the microwave range (SHF) have a length of 300 mm to 1 mm. Centimeter waves, like decimeter and meter radio waves, are practically not absorbed by the atmosphere and are therefore widely used in satellites.
kovoy and cellular communication and other telecommunication systems. The size of a typical satellite dish is just equal to several wavelengths of such waves.
Shorter microwaves also have many applications in industry and in the home. Suffice it to mention microwave ovens, which today are equipped with both industrial bakeries and home kitchens. The operation of a microwave oven is based on the rapid rotation of electrons in a device called a klystron. As a result, the electrons emit electromagnetic microwaves of a certain frequency, at which they are easily absorbed by water molecules. When you put food in the microwave, the water molecules in the food absorb the energy of the microwaves, move faster, and thus heat up the food. In other words, unlike a conventional oven or oven, where food is heated from the outside, a microwave oven heats it from the inside.
infrared rays
This part of the electromagnetic spectrum includes radiation with a wavelength from 1 millimeter to eight thousand atomic diameters (about 800 nm). A person feels the rays of this part of the spectrum directly with the skin - as heat. If you stretch your hand in the direction of a fire or a red-hot object and feel the heat emanating from it, you perceive infrared radiation as heat. Some animals (for example, burrowing vipers) even have sensory organs that allow them to locate warm-blooded prey by infrared radiation from its body.
Since most objects on the Earth's surface emit energy in the infrared wavelength range, infrared detectors play an important role in modern detection technologies. Infrared eyepieces of night vision devices allow people to "see in the dark", and with their help it is possible to detect not only people, but also equipment and structures that have heated up during the day and give off their heat to the environment at night in the form of infrared rays. Infrared detectors are widely used by rescue services, for example, to detect living people under the rubble after earthquakes or other natural and man-made disasters.
visible light
As already mentioned, the wavelengths of electromagnetic waves in the visible light range range from eight to four thousand atomic diameters (800-400 nm). The human eye is an ideal tool for recording and analyzing electromagnetic waves in this range. This is due to two reasons. First, as noted, the waves of the visible part of the spectrum propagate practically unhindered in an atmosphere that is transparent to them. Secondly, the temperature of the Sun's surface (about 5000°C) is such that the peak of solar energy is in the visible part of the spectrum. Thus, our main source of energy emits a huge amount of energy in the visible light range, and the environment around us is largely transparent to this radiation. It is not surprising, therefore, that the human eye in the process of evolution was formed in such a way as to capture and recognize this particular part of the spectrum of electromagnetic waves.
I want to emphasize once again that there is nothing special from a physical point of view in the range of visible electromagnetic rays. It is just a narrow strip in a wide spectrum of emitted waves (see figure). For us, it is so important only insofar as the human brain is equipped with a tool for detecting and analyzing electromagnetic waves in this particular part of the spectrum.
Ultra-violet rays
Ultraviolet rays include electromagnetic radiation with a wavelength from several thousand to several atomic diameters (400-10 nm). In this part of the spectrum, radiation begins to affect the vital activity of living organisms. Soft ultraviolet rays in the solar spectrum (with wavelengths approaching the visible part of the spectrum), for example, cause tanning in moderate doses, and severe burns in excess. Hard (short-wavelength) ultraviolet is harmful to biological cells and is therefore used, in particular, in medicine to sterilize surgical instruments and medical equipment, killing all microorganisms on their surface.
All life on Earth is protected from the harmful effects of hard ultraviolet radiation by the ozone layer of the earth's atmosphere, which absorbs most of the hard ultraviolet rays in the solar radiation spectrum (see the ozone hole). If not for this natural shield, life on Earth would hardly have come to land from the waters of the oceans. However, despite the protective ozone layer, some of the hard ultraviolet rays reach the Earth's surface and can cause skin cancer, especially in people who are naturally prone to pallor and do not tan well in the sun.
X-rays
Radiation in the wavelength range from several atomic diameters to several hundred diameters of the atomic nucleus is called x-rays. X-rays penetrate the soft tissues of the body and are therefore indispensable in medical diagnosis.
tick. As in the case of radio waves, the time gap between their discovery in 1895 and the beginning of practical application, marked by the receipt of the first x-ray in one of the Parisian hospitals, was a matter of years. (It is interesting to note that the Parisian newspapers of the time were so engrossed in the idea that X-rays could penetrate clothing that they reported virtually nothing about their unique medical applications.)
gamma rays
The shortest in wavelength and the highest in frequency and energy rays in the electromagnetic spectrum are y-rays (gamma rays). They consist of ultrahigh-energy photons and are used today in oncology to treat cancerous tumors (or rather, to kill cancer cells). However, their effect on living cells is so destructive that extreme care must be taken in order not to harm the surrounding healthy tissues and organs.
In conclusion, it is important to emphasize once again that, although all the types of electromagnetic radiation described above manifest themselves outwardly in different ways, in essence they are twins. All electromagnetic waves in any part of the spectrum are transverse oscillations of electric and magnetic fields propagating in vacuum or in a medium, they all propagate in vacuum at the speed of light c and differ from each other only in their wavelength and, as a result, in the energy they carry. It only remains to add that the boundaries of the ranges I have named are of a rather arbitrary nature (and in other books you will most likely come across slightly different values of the boundary wavelengths). In particular, microwave radiation with long wavelengths is often and rightly referred to as microwave radio waves. There are no clear boundaries between hard ultraviolet and soft X-rays, and between hard X-rays and soft gamma radiation.
Spectroscopy
The presence of atoms of chemical elements in a substance can be identified by the presence of characteristic lines in the emission or absorption spectrum
Properties of electromagnetic radiation. Electromagnetic radiations with different wavelengths have quite a few differences, but all of them, from radio waves to gamma radiation, are of the same physical nature. All types of electromagnetic radiation, to a greater or lesser extent, exhibit the properties of interference, diffraction and polarization characteristic of waves. At the same time, all types of electromagnetic radiation exhibit quantum properties to a greater or lesser extent.
Common to all electromagnetic radiation are the mechanisms of their occurrence: electromagnetic waves with any wavelength can occur during the accelerated movement of electric charges or during the transitions of molecules, atoms or atomic nuclei from one quantum state to another. Harmonic oscillations of electric charges are accompanied by electromagnetic radiation having a frequency equal to the frequency of charge oscillations.
Radio waves. With oscillations occurring at frequencies from 10 5 to 10 12 Hz, electromagnetic radiation occurs, the wavelengths of which lie in the range from several kilometers to several millimeters. This section of the electromagnetic radiation scale refers to the radio wave range. Radio waves are used for radio communications, television, and radar.
Infrared radiation. Electromagnetic radiation with a wavelength less than 1-2 mm, but greater than 8 * 10 -7 m, i.e. lying between the range of radio waves and the range of visible light are called infrared radiation.
The region of the spectrum beyond its red edge was first experimentally investigated in 1800. English astronomer William Herschel (1738-1822). Herschel placed the black bulb thermometer beyond the red end of the spectrum and detected an increase in temperature. The thermometer bulb was heated by radiation, invisible to the eye. This radiation is called infrared rays.
Infrared radiation is emitted by any heated body. Sources of infrared radiation are stoves, water heaters, electric incandescent lamps.
With the help of special devices, infrared radiation can be converted into visible light and images of heated objects can be obtained in complete darkness. Infrared radiation is used for drying painted products, building walls, wood.
visible light. Visible light (or simply light) includes radiation with a wavelength of approximately 8*10-7 to 4*10-7 m, from red to violet light.
The significance of this part of the spectrum of electromagnetic radiation in human life is exceptionally great, since a person receives almost all information about the world around him with the help of vision.
Light is a prerequisite for the development of green plants and, therefore, a necessary condition for the existence of life on Earth.
Ultraviolet radiation. In 1801, the German physicist Johann Ritter (1776 - 1810), while studying the spectrum, discovered that beyond its violet edge there is an area created by rays invisible to the eye. These rays affect certain chemical compounds. Under the action of these invisible rays, the decomposition of silver chloride occurs, the glow of zinc sulfide crystals and some other crystals.
Electromagnetic radiation that is invisible to the eye and has a wavelength shorter than violet light is called ultraviolet radiation. Ultraviolet radiation includes electromagnetic radiation in the wavelength range from 4 * 10 -7 to 1 * 10 -8 m.
Ultraviolet radiation is capable of killing pathogenic bacteria, so it is widely used in medicine. Ultraviolet radiation in the composition of sunlight causes biological processes that lead to darkening of human skin - sunburn.
Discharge lamps are used as sources of ultraviolet radiation in medicine. The tubes of such lamps are made of quartz, transparent to ultraviolet rays; therefore these lamps are called quartz lamps.
X-rays. If a constant voltage of several tens of thousands of volts is applied in a vacuum tube between a heated cathode that emits an electron and an anode, then the electrons will first be accelerated by an electric field, and then sharply decelerated in the anode substance when interacting with its atoms. During deceleration of fast electrons in a substance or during electron transitions on the inner shells of atoms, electromagnetic waves arise with a wavelength shorter than that of ultraviolet radiation. This radiation was discovered in 1895 by the German physicist Wilhelm Roentgen (1845-1923). Electromagnetic radiation in the wavelength range from 10 -14 to 10 -7 m are called x-rays.
X-rays are invisible to the eye. They pass without significant absorption through significant layers of material that is opaque to visible light. X-rays are detected by their ability to cause a certain glow of certain crystals and act on photographic film.
The ability of X-rays to penetrate through thick layers of matter is used to diagnose diseases of human internal organs. In engineering, X-rays are used to control the internal structure of various products, welds. X-ray radiation has a strong biological effect and is used to treat certain diseases.
Gamma radiation. Gamma radiation is called electromagnetic radiation emitted by excited atomic nuclei and arising from the interaction of elementary particles.
Gamma radiation is the shortest wavelength electromagnetic radiation (l < 10 -10 m). Its feature is pronounced corpuscular properties. Therefore, gamma radiation is usually considered as a stream of particles - gamma rays. In the region of wavelengths from 10 -10 to 10 -14 and the ranges of x-rays and gamma radiation overlap, in this region, x-rays and gamma rays are identical in nature and differ only in origin.
Types of radiation
thermal radiation – radiation, in which the loss of energy by atoms for the emission of light is compensated for by the energy of the thermal motion of the atoms (or molecules) of the radiating body. The heat source is the sun, an incandescent lamp, etc.
electroluminescence(from the Latin luminescence - "glow") - a discharge in a gas accompanied by a glow. The northern lights are a manifestation of electroluminescence. Used in tubes for advertising inscriptions.
cathodoluminescence– the glow of solids caused by their bombardment by electrons. Thanks to her, the screens of cathode ray tubes of TVs glow.
Chemiluminescence– the emission of light in some chemical reactions with the release of energy. It can be observed on the example of a firefly and other living organisms that have the property of glowing.
Photoluminescence– the glow of bodies directly under the action of radiation falling on them. An example is the luminous paints that cover Christmas decorations, they emit light after being irradiated. This phenomenon is widely used in daylight lamps.
In order for an atom to begin to radiate, it needs to transfer a certain amount of energy. By radiating, an atom loses the energy it has received, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary.
Spectra
Striped Spectra
The striped spectrum consists of individual bands separated by dark gaps. With the help of a very good spectral apparatus, it can be found that each band is a collection of a large number of very closely spaced lines. Unlike line spectra, striped spectra are produced not by atoms, but by molecules that are not bonded or weakly bonded to each other.
To observe molecular spectra, as well as to observe line spectra, one usually uses the glow of vapors in a flame or the glow of a gas discharge.
Spectral analysis
Spectral analysis is a set of methods for qualitative and quantitative determination of the composition of an object, based on the study of the spectra of the interaction of matter with radiation, including the spectra of electromagnetic radiation, acoustic waves, the mass and energy distribution of elementary particles, etc. Depending on the goals of the analysis and the types of spectra, several methods are distinguished spectral analysis. Atomic and molecular spectral analyzes make it possible to determine the elemental and molecular composition of a substance, respectively. In the emission and absorption methods, the composition is determined from the emission and absorption spectra. Mass spectrometric analysis is carried out using the mass spectra of atomic or molecular ions and makes it possible to determine the isotopic composition of an object. The simplest spectral apparatus is a spectrograph.
Scheme of the device of a prism spectrograph
Story
Dark lines on spectral stripes were noticed long ago (for example, they were noted by Wollaston), but the first serious study of these lines was undertaken only in 1814 by Josef Fraunhofer. The effect was named Fraunhofer Lines in his honor. Fraunhofer established the stability of the position of the lines, compiled their table (he counted 574 lines in total), assigned an alphanumeric code to each. No less important was his conclusion that the lines are not associated with either optical material or the earth's atmosphere, but are a natural characteristic of sunlight. He found similar lines in artificial light sources, as well as in the spectra of Venus and Sirius.
Fraunhofer lines
To test the method in 1868, the Paris Academy of Sciences organized an expedition to India, where a total solar eclipse was coming. There, scientists found that all the dark lines at the time of the eclipse, when the emission spectrum changed the absorption spectrum of the solar corona, became, as predicted, bright against a dark background.
The nature of each of the lines, their connection with the chemical elements were gradually elucidated. In 1860, Kirchhoff and Bunsen, using spectral analysis, discovered cesium, and in 1861, rubidium. And helium was discovered on the Sun 27 years earlier than on Earth (1868 and 1895, respectively).
Principle of operation
The atoms of each chemical element have strictly defined resonant frequencies, as a result of which it is at these frequencies that they emit or absorb light. This leads to the fact that in the spectroscope, lines (dark or light) are visible on the spectra in certain places characteristic of each substance. The intensity of the lines depends on the amount of matter and its state. In quantitative spectral analysis, the content of the test substance is determined by the relative or absolute intensities of lines or bands in the spectra.
Optical spectral analysis is characterized by relative ease of implementation, the absence of complicated preparation of samples for analysis, and a small amount of a substance (10–30 mg) required for analysis for a large number of elements. Atomic spectra (absorption or emission) are obtained by transferring a substance to a vapor state by heating the sample to 1000-10000 °C. As sources of excitation of atoms in the emission analysis of conductive materials, a spark, an alternating current arc are used; while the sample is placed in the crater of one of the carbon electrodes. Flames or plasmas of various gases are widely used to analyze solutions.
Spectrum of electromagnetic radiation
Properties of electromagnetic radiation. Electromagnetic radiations with different wavelengths have quite a few differences, but all of them, from radio waves to gamma radiation, are of the same physical nature. All types of electromagnetic radiation, to a greater or lesser extent, exhibit the properties of interference, diffraction and polarization characteristic of waves. At the same time, all types of electromagnetic radiation exhibit quantum properties to a greater or lesser extent.
Common to all electromagnetic radiation are the mechanisms of their occurrence: electromagnetic waves with any wavelength can occur during the accelerated movement of electric charges or during the transitions of molecules, atoms or atomic nuclei from one quantum state to another. Harmonic oscillations of electric charges are accompanied by electromagnetic radiation having a frequency equal to the frequency of charge oscillations.
radio waves. With oscillations occurring at frequencies from 10 5 to 10 12 Hz, electromagnetic radiation occurs, the wavelengths of which lie in the range from several kilometers to several millimeters. This section of the electromagnetic radiation scale refers to the radio wave range. Radio waves are used for radio communications, television, and radar.
Infrared radiation. Electromagnetic radiation with a wavelength less than 1-2 mm, but greater than 8 * 10 -7 m, i.e. lying between the range of radio waves and the range of visible light are called infrared radiation.
Infrared radiation is emitted by any heated body. Sources of infrared radiation are stoves, water heaters, electric incandescent lamps.
With the help of special devices, infrared radiation can be converted into visible light and images of heated objects can be obtained in complete darkness. Infrared radiation is used for drying painted products, building walls, wood.
visible light.Visible light (or simply light) includes radiation with a wavelength of approximately 8*10 -7 to 4*10 -7 m, from red to violet light.
The significance of this part of the spectrum of electromagnetic radiation in human life is exceptionally great, since a person receives almost all information about the world around him with the help of vision. Light is a prerequisite for the development of green plants and, therefore, a necessary condition for the existence of life on Earth.
Ultraviolet radiation. In 1801, the German physicist Johann Ritter (1776 - 1810), while studying the spectrum, discovered that
Electromagnetic radiation that is invisible to the eye and has a wavelength shorter than violet light is called ultraviolet radiation. Ultraviolet radiation includes electromagnetic radiation in the wavelength range from 4 * 10 -7 to 1 * 10 -8 m.
Ultraviolet radiation is capable of killing pathogenic bacteria, so it is widely used in medicine. Ultraviolet radiation in the composition of sunlight causes biological processes that lead to darkening of human skin - sunburn.
Discharge lamps are used as sources of ultraviolet radiation in medicine. The tubes of such lamps are made of quartz, transparent to ultraviolet rays; therefore these lamps are called quartz lamps.
X-rays. If a constant voltage of several tens of thousands of volts is applied in a vacuum tube between a heated cathode that emits an electron and an anode, then the electrons will first be accelerated by an electric field, and then sharply decelerated in the anode substance when interacting with its atoms. During deceleration of fast electrons in a substance or during electron transitions on the inner shells of atoms, electromagnetic waves arise with a wavelength shorter than that of ultraviolet radiation. This radiation was discovered in 1895 by the German physicist Wilhelm Roentgen (1845-1923). Electromagnetic radiation in the wavelength range from 10 -14 to 10 -7 m are called x-rays.
The ability of X-rays to penetrate through thick layers of matter is used to diagnose diseases of human internal organs. In engineering, X-rays are used to control the internal structure of various products, welds. X-ray radiation has a strong biological effect and is used to treat certain diseases. Gamma radiation. Gamma radiation is called electromagnetic radiation emitted by excited atomic nuclei and arising from the interaction of elementary particles.
Gamma radiation- the shortest wavelength electromagnetic radiation (<10 -10 м). Его особенностью являются ярко выраженные корпускулярные свойства. Поэтому гамма-излучение обычно рассматривают как поток частиц - гамма-квантов. В области длин волн от 10 -10 до 10 -14 и диапазоны рентгеновского и гамма-излучений перекрываются, в этой области рентгеновские лучи и гамма-кванты по своей природе тождественны и отличаются лишь происхождением.
The theory shows that electromagnetic radiation is formed when electric charges move unevenly, accelerated. A uniformly moving (free) flow of electric charges does not radiate. There is no radiation of an electromagnetic field for charges moving under the action of a constant force, for example, for charges describing a circle in a magnetic field.
In oscillatory movements, the acceleration is constantly changing, so the oscillations of electric charges give off electromagnetic radiation. In addition, electromagnetic radiation will occur during a sharp non-uniform deceleration of charges, for example, when an electron beam hits an obstacle (formation of X-ray beams). In the chaotic thermal motion of particles, electromagnetic radiation (thermal radiation) is also born. Ripple
nuclear charge lead to the creation of electromagnetic radiation, known as y-rays. Ultraviolet rays and visible light are produced by the movement of atomic electrons. Fluctuations of electric charge on a cosmic scale lead to radio emission from celestial bodies.
Along with natural processes that create electromagnetic radiation of various properties, there are various experimental possibilities for creating electromagnetic radiation.
The main characteristic of electromagnetic radiation is its frequency (if we are talking about harmonic oscillation) or frequency band. It is false, of course, to recalculate the frequency of radiation by the length of an electromagnetic wave in a vacuum using the relation.
The radiation intensity is proportional to the fourth power of the frequency. Therefore, radiation of very low frequencies with wavelengths of the order of hundreds of kilometers is not traced. The practical radio range begins, as you know, with wavelengths of the order of magnitude, which corresponds to frequencies of the order of wavelengths of the order referred to the middle range, tens of meters are already short waves. Ultrashort waves (VHF) take us out of the normal radio range; wavelengths of the order of several meters and fractions of a meter up to a centimeter (i.e., frequencies of the order are used in television and radar.
Even shorter electromagnetic waves were obtained in 1924 by Glagoleva-Arkadyeva. She used as a generator electrical sparks between iron filings suspended in oil, and received waves up to 1000. Here overlap with the wavelengths of thermal radiation is already achieved.
The area of visible light is very small: it occupies only wavelengths from cm to cm. Next are ultraviolet rays, invisible to the eye, but very well fixed by physical instruments. This is the wavelength from cm to cm.
Ultraviolet is followed by x-rays. Their wavelengths are from cm to cm. The shorter the wavelength, the weaker the X-rays are absorbed by substances. The most short-wavelength and penetrating electromagnetic radiation is called y-rays (wavelengths from cm and below).
The characteristic of any kind of the listed electromagnetic radiations will be exhaustive if the following measurements are made. First of all, by one method or another, electromagnetic radiation must be decomposed into a spectrum. In the case of light, ultraviolet rays and infrared radiation, this can be done by refraction by a prism or by passing the radiation through a diffraction grating (see below). In the case of x-rays and gamma rays, the expansion into a spectrum is achieved by reflection from the crystal (see p. 351). Waves
radio range are decomposed into a spectrum using the phenomenon of resonance.
The resulting emission spectrum can be continuous or lined, i.e., can continuously fill a certain frequency band, and can also consist of separate sharp lines corresponding to an extremely narrow frequency interval. In the first case, to characterize the spectrum, it is necessary to set the intensity curve as a function of frequency (wavelength), in the second case, the spectrum will be described by setting all the lines present in it, indicating their frequencies and intensities.
Experience shows that electromagnetic radiation of a given frequency and intensity can differ in its polarization state. Along with waves in which the electric vector oscillates along a certain line (linearly polarized waves), one has to deal with radiation in which linearly polarized waves rotated with respect to each other about the beam axis are superimposed on each other. With an exhaustive characterization of radiation, it is necessary to indicate its polarization.
It should be noted that even for the slowest electromagnetic oscillations, we are unable to measure the electric and magnetic vectors of the wave. The field pictures drawn above are theoretical in nature. Nevertheless, there is no doubt about their truth, bearing in mind the continuity and integrity of the entire electromagnetic theory.
The assertion that one or another type of radiation belongs to electromagnetic waves is always indirect. However, the number of consequences arising from the hypotheses is so huge and they are in such close agreement with each other that the hypothesis of the electromagnetic spectrum has long acquired all the features of immediate reality.
