Radiation and spectra. electromagnetic spectrum

The range of frequencies emitted by electromagnetic waves is huge. It is determined by all possible frequencies of oscillations of charged particles. Such oscillations occur with alternating current in power lines, antennas of radio and television stations, mobile phones, radars, lasers, incandescent lamps 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 in connection with this find various applications in radio communications and 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.

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 a substance, 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 radiated into infrared range. 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, missing electricity 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.

The electromagnetic spectrum is conditionally divided into ranges. As a result of their consideration, you need to know the following.

• The name of the ranges of electromagnetic waves.
• The order in which they follow.
• Range boundaries in wavelengths or frequencies.
• What causes the absorption or emission of waves of one or another range.
• The use of each type of electromagnetic waves.
• Sources of radiation of various electromagnetic waves (natural and artificial).
• Danger of every kind of waves.
• Examples of objects that have dimensions comparable to the wavelength of the corresponding range.
• The concept of black body radiation.
• Solar radiation and atmospheric transparency windows.

Ranges of electromagnetic waves

microwave range

Microwaves are used to heat food in microwave ovens, mobile communications, radars (radar), up to 300 GHz easily passes the atmosphere, therefore it is suitable for satellite communications. Radiometers for remote sensing and determining the temperature of different layers of the atmosphere, as well as radio telescopes, operate in this range. This range is one of the key ones for EPR spectroscopy and rotational spectra of molecules. Prolonged exposure to the eyes causes cataracts. Cell phones negatively affect the brain.

A characteristic feature of microwave waves is that their wavelength is comparable to the size of the equipment. Therefore, in this range, devices are designed on the basis of distributed elements. Waveguides and strip lines are used for energy transmission, and cavity resonators or resonant lines are used as resonant elements. Man-made sources of MW waves are klystrons, magnetrons, traveling wave tubes (TWTs), Gunn diodes, and avalanche transit diodes (ATDs). In addition, there are masers, analogues of lasers in the long wavelength ranges.

Microwave waves are emitted by stars.

In the microwave range is the so-called cosmic background microwave radiation (relic radiation), which in its spectral characteristics fully corresponds to the radiation of a completely black body with a temperature of 2.72K. The maximum of its intensity falls at a frequency of 160 GHz (1.9 mm) (see figure below). The presence of this radiation and its parameters are one of the arguments in favor of the Big Bang theory, which is currently the basis of modern cosmology. The last one, according to these measurements and observations in particular, occurred 13.6 billion years ago.

Above 300 GHz (shorter than 1 mm), electromagnetic waves are very strongly absorbed by the Earth's atmosphere. The atmosphere begins to be transparent in the IR and visible ranges.

Among the lasers and sources with their application, emitting in the visible range, the following can be mentioned: the first launched laser, - ruby, with a wavelength of 694.3 nm, diode lasers, for example, based on GaInP and AlGaInP for the red range, and based on GaN for the blue range, titanium-sapphire laser, He-Ne laser, argon and krypton ion lasers, copper vapor laser, dye lasers, lasers with frequency doubling or frequency summation in nonlinear media, Raman lasers. (https://www.rp-photonics.com/visible_lasers.html?s=ak).

For a long time there was a problem in creating compact lasers in the blue-green part of the spectrum. There were gas lasers such as argon ion laser(since 1964), in which two main generation lines lie in the blue and green parts of the spectrum (488 and 514 nm) or a helium-cadmium laser. However, they were not suitable for many applications due to their bulkiness and the limited number of generation lines. It was not possible to create semiconductor lasers with a wide bandgap due to enormous technological difficulties. However, eventually developed effective methods doubling and tripling the frequency of solid-state lasers in the IR and optical range in nonlinear crystals, semiconductor lasers based on double GaN compounds and lasers with an increase in the pump frequency (upconversion lasers).

Light sources in the blue-green region allow to increase the recording density on a CD-ROM, the quality of reprographics, are necessary for creating full-color projectors, for communicating with submarines, for removing seabed topography, for laser cooling individual atoms and ions, to control vapor deposition, in flow cytometry. (taken from “Compact blue-green lasers” by W. P. Risk et al).

Literature:

UV range

It is believed that the ultraviolet range occupies the region from 10 to 380 nm. Although its boundaries are not clearly defined, especially in the shortwave region. It is divided into sub-ranges and this division is also not unambiguous, since in different sources it is tied to various physical and biological processes.

So on the website of the "Health Physics Society" the ultraviolet range is defined within the limits of 40 - 400 nm and is divided into five subranges: vacuum UV (40-190 nm), far UV (190-220 nm), UVC (220-290 nm), UVB (290-320 nm), and UVA (320-400 nm) (black light). In the English version of the Wikipedia article on ultraviolet "Ultraviolet", the range of 40 - 400 nm is allocated to ultraviolet radiation, however, in the table in the text it is divided into a bunch of overlapping subranges, starting from 10 nm. In the Russian-language version of Wikipedia "Ultraviolet radiation" from the very beginning, the limits of the UV range are set within 10 - 400 nm. In addition, Wikipedia for the UVC, UVB and UVA ranges indicates the areas 100 - 280, 280 - 315, 315 - 400 nm.

Ultraviolet radiation, despite its beneficial effect in small quantities on biological objects is at the same time the most dangerous of all other natural widespread radiation in other ranges.

The main natural source of UV radiation is the Sun. However, not all radiation reaches the Earth, since it is absorbed by the ozone layer of the stratosphere and, in the region shorter than 200 nm, is very strongly absorbed by atmospheric oxygen.

UVC is almost completely absorbed by the atmosphere and does not reach the earth's surface. This range is used by germicidal lamps. Overexposure results in corneal damage and snow blindness, as well as severe facial burns.

UVB is the most damaging part of UV radiation as it has enough energy to damage DNA. It is not completely absorbed by the atmosphere (about 2% passes). This radiation is necessary for the production (synthesis) of vitamin D, but the harmful effects can cause burns, cataracts and skin cancer. This part of the radiation is absorbed by atmospheric ozone, the decline of which is a cause for concern.

UVA almost completely reaches the Earth (99%). It is responsible for sunburn, but excess leads to burns. Like UVB, it is necessary for the synthesis of vitamin D. Excessive exposure leads to immune system suppression, skin stiffness, and cataract formation. Radiation in this range is also called black light. Insects and birds are able to see this light.

The figure below shows, for example, the dependence of ozone concentration on height at northern latitudes (yellow curve) and the level of blocking of solar ultraviolet by ozone. UVC is completely absorbed up to altitudes of 35 km. At the same time, UVA almost completely reaches the Earth's surface, but this radiation poses practically no danger. Ozone traps most of the UVB, but some reaches the Earth. In the event of depletion of the ozone layer, most of it will irradiate the surface and lead to genetic damage to living beings.

Brief list of uses of electromagnetic waves in the UV range.

• High quality photolithography for the manufacture of electronic devices such as microprocessors and memory chips.
• In the manufacture of fiber optic elements, in particular Bragg gratings.
• Disinfection from microbes of products, water, air, objects (UVC).
• Black light (UVA) in forensics, in the examination of works of art, in the establishment of the authenticity of banknotes (fluorescence phenomenon).
• Artificial tan.
• Laser engraving.
• Dermatology.
• Dentistry (photopolymerization of fillings).

Man-made sources of ultraviolet radiation are:

Non-monochromatic: Mercury discharge lamps various pressures and designs.

Monochromatic:

1. Laser diodes, mainly based on GaN, (low power), generating in the near ultraviolet range;
2. Excimer lasers are very powerful sources of ultraviolet radiation. They emit nanosecond (picosecond and microsecond) pulses with an average power ranging from a few watts to hundreds of watts. Typical wavelengths lie between 157 nm (F2) to 351 nm (XeF);
3. Some solid-state lasers doped with cerium, such as Ce3+:LiCAF or Ce3+:LiLuF4, which are pulsed with nanosecond pulses;
4. Some fiber lasers, such as those doped with neodymium;
5. Some dye lasers are capable of emitting ultraviolet light;
6. Ion argon laser, which, despite the fact that the main lines lie in the optical range, can generate continuous radiation with wavelengths of 334 and 351 nm, but with lower power;
7. Nitrogen laser emitting at a wavelength of 337 nm. A very simple and cheap laser, operates in a pulsed mode with a nanosecond pulse duration and with a peak power of several megawatts;
8. Triple frequencies of Nd:YAG laser in nonlinear crystals;

Literature:

1. Wikipedia "Ultraviolet".

Given in a separate article;

The transparency of a substance for gamma rays, unlike visible light, does not depend on the chemical form and state of aggregation matter, but mainly from the charge of the nuclei that make up the substance, and from the energy of gamma rays. Therefore, the absorption capacity of a substance layer for gamma quanta in the first approximation can be characterized by its surface density (in g/cm²). For a long time it was believed that the creation of mirrors and lenses for γ-rays is impossible, however, according to the latest research in this field, the refraction of γ-rays is possible. This discovery, perhaps, means the creation of a new branch of optics - γ-optics.

sharp lower bound for gamma radiation does not exist, but it is usually believed that gamma quanta are emitted by the nucleus, and x-ray quanta - by the electron shell of the atom (this is only a terminological difference that does not affect physical properties radiation).

x-ray radiation

• from 0.1 nm = 1 Å (12,400 eV) to 0.01 nm = 0.1 Å (124,000 eV) - hard x-rays. Sources: some nuclear reactions, cathode ray tubes.
• from 10 nm (124 eV) to 0.1 nm = 1 Å (12,400 eV) - soft x-rays. Sources: cathode ray tubes, thermal radiation plasma.

X-ray quanta are emitted mainly during the transitions of electrons in the electron shell of heavy atoms to low-lying orbits. Vacancies in low-lying orbits are usually created by electron impact. x-ray radiation, created in this way, has a line spectrum with frequencies characteristic of a given atom (see Fig. characteristic radiation); this makes it possible, in particular, to investigate the composition of substances (X-ray fluorescence analysis). Thermal, bremsstrahlung, and synchrotron X-rays have a continuous spectrum.

In x-rays, diffraction on crystal lattices is observed, since the wavelengths of electromagnetic waves at these frequencies are close to the periods of crystal lattices. The method of X-ray diffraction analysis is based on this.

Ultraviolet radiation

Range: 400 nm (3.10 eV) to 10 nm (124 eV)

optical radiation

Radiation of the optical range (visible light and near infrared [ ]) freely passes through the atmosphere, can be easily reflected and refracted in optical systems. Sources: thermal radiation (including the Sun), fluorescence, chemical reactions, LEDs.

The colors of visible radiation corresponding to monochromatic radiation are called spectral. The spectrum and spectral colors can be seen when a narrow beam of light passes through a prism or some other refractive medium. Traditionally, the visible spectrum is divided, in turn, into ranges of colors:

Middle infrared radiation occupies the range from 207 THz (0.857 eV) to 405 THz (1.68 eV). The upper limit is determined by the ability of the human eye to perceive red, which varies from person to person. As a rule, the transparency in the near infrared radiation corresponds to the transparency in visible light.

Infrared radiation

Infrared radiation is located between visible light and terahertz radiation. Range: 2000 µm (150 GHz) to 740 nm (405 THz).

The theory shows that electromagnetic radiation It 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 O 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.

followed by ultraviolet 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 the waves, which 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.

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– light emission in some chemical reactions going 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, stripe spectra are created not by atoms, but by molecules that are not bound or weakly bound. bound friend with a friend.

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

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 full solar eclipse. 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 thick layers of matter is used to diagnose diseases. internal organs person. 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.