Electromagnetic waves (the table of which will be given below) are perturbations of magnetic and electric fields distributed in space. There are several types. The study of these perturbations is done by physics. Electromagnetic waves are generated due to the fact that an alternating electric field generates a magnetic field, and it, in turn, generates an electric field.
Research history
The first theories, which can be considered the oldest versions of the hypotheses about electromagnetic waves, relate at least to the Huygens times. At that time, assumptions reached a pronounced quantitative development. Huygens in 1678 released a kind of "sketch" of the theory - "Treatise on Light." In 1690, he also published another remarkable work. It laid out the qualitative theory of reflection, refraction in the form in which it is still presented in school textbooks ("Electromagnetic waves", grade 9).
Along with this, the Huygens principle was formulated. With its help, it became possible to study the motion of the wave front. This principle subsequently found its development in the works of Fresnel. The Huygens-Fresnel principle was of particular importance in the theory of diffraction and the wave theory of light.
In the 1660-1670s, a great experimental and theoretical contribution was made to the studies of Hook and Newton. Who discovered electromagnetic waves? Who conducted the experiments proving their existence? What types of electromagnetic waves are there? About it further.
Justification of Maxwell
Before talking about who discovered the electromagnetic waves, it should be said that the first scientist who generally predicted their existence was Faraday. He put forward his hypothesis in 1832. Maxwell subsequently engaged in the construction of the theory. By 1865, he completed this work. As a result, Maxwell strictly formalized the theory mathematically, justifying the existence of the phenomena under consideration. He also determined the propagation velocity of electromagnetic waves, which coincided with the value of light speed used then. This, in turn, allowed him to substantiate the hypothesis that light is one of the types of radiation under consideration.
Experimental discovery
Maxwell's theory was confirmed in the experiments of Hertz in 1888. It should be said here that the German physicist conducted his experiments in order to refute the theory, despite its mathematical justification. However, thanks to his experiments, Hertz was the first to discover electromagnetic waves in practice. In addition, during his experiments, the scientist revealed the properties and characteristics of radiation.
Hertz received electromagnetic oscillations and waves due to the excitation of a series of pulses of a rapidly varying flow in a vibrator using a source of increased voltage. High-frequency streams can be detected using a loop. The oscillation frequency will be the higher, the higher its capacitance and inductance. But at the same time, a high frequency is not a guarantee of intense flow. To carry out his experiments, Hertz used a fairly simple device, which today is called the "Hertz vibrator." The device is an open circuit oscillatory type.
Hertz's Experience Scheme
Registration of radiation was carried out using a receiving vibrator. This device had the same design as the radiating device. Under the influence of an electromagnetic wave of an electric alternating field, a current oscillation was excited in the receiving device. If in this device its natural frequency and the frequency of the flow coincided, then a resonance appeared. As a result, disturbances in the receiving device occurred with a larger amplitude. The researcher discovered them, observing the sparks between the conductors in a small gap.
Thus, Hertz was the first to discover electromagnetic waves, proved their ability to reflect well from conductors. He was practically justified by the formation of standing radiation. In addition, Hertz determined the speed of propagation of electromagnetic waves in air.
Character study
Electromagnetic waves propagate in almost all environments. In a space that is filled with matter, radiation can in some cases be distributed fairly well. But at the same time, they slightly change their behavior.
Electromagnetic waves in a vacuum are detected without attenuation. They are distributed at any arbitrarily large distance. The main characteristics of the waves include polarization, frequency and length. The description of the properties is carried out in the framework of electrodynamics. However, the characteristics of the radiation of some regions of the spectrum are dealt with by more specific sections of physics. These, for example, include optics.
The study of hard electromagnetic radiation from the short-wavelength spectral end is carried out by the high-energy section. Given modern ideas, dynamics ceases to be an independent discipline and combines with weak interactions in one theory.
Theories used in the study of properties
Today, there are various methods that contribute to the modeling and study of the manifestations and properties of oscillations. The most fundamental of the tested and completed theories is quantum electrodynamics. From it, through various simplifications, it becomes possible to obtain the methods listed below, which are widely used in various fields.
The description of relatively low-frequency radiation in a macroscopic medium is carried out using classical electrodynamics. It is based on Maxwell's equations. At the same time, there are simplifications in applied applications. In optical studies, optics are used. The wave theory is applied in cases when some parts of the optical system are close in size to wavelengths. Quantum optics is used when the processes of scattering and absorption of photons are significant.
Geometric optical theory is the ultimate case in which wavelength neglect is allowed. There are also several applied and fundamental sections. For example, they include astrophysics, biology of visual perception and photosynthesis, and photochemistry. How are electromagnetic waves classified? A table illustrating the distribution of groups is presented below.
Classification
There are frequency ranges of electromagnetic waves. There are no sharp transitions between them, sometimes they overlap each other. The boundaries between them are rather arbitrary. Due to the fact that the flow is distributed continuously, the frequency is rigidly associated with the length. Below are the ranges of electromagnetic waves.
| Title | Length | Frequency |
| Gamma | Less than 5 pm | more than 6 • 1019 Hz |
| Roentgen | 10 nm - 5 pm | 3 • 1016-6 • 1019 Hz |
| Ultraviolet | 380 - 10 nm | 7.5 • 1014-3 • 1016 Hz |
| Visible radiation | 780 to 380 nm | 429-750 THz |
| Infrared radiation | 1 mm - 780 nm | 330 GHz-429 THz |
| Ultra short | 10 m - 1 mm | 30 MHz-300 GHz |
| A short | 100 m - 10 m | 3-30 MHz |
| Average | 1 km - 100 m | 300kHz-3MHz |
| Long | 10 km - 1 km | 30-300 kHz |
| Extra Long | More than 10 km | Less than 30 kHz |
Ultrashort radiation is usually divided into micrometer (submillimeter), millimeter, centimeter, decimeter, meter. If the wavelength of electromagnetic radiation is less than a meter, then it is commonly called oscillation of superhigh frequency (microwave).
Types of electromagnetic waves
The ranges of electromagnetic waves are presented above. What types of flows are there? The group of ionizing radiation includes gamma and x-rays. It should be said that ultraviolet and even visible light are capable of ionizing atoms. The boundaries in which gamma and X-ray fluxes are located are determined very conditionally. The limits of 20 eV - 0.1 MeV are accepted as a general orientation. Gamma-ray fluxes in the narrow sense are emitted by the nucleus, X-ray fluxes are emitted by the electron atomic shell during knocking out electrons from low-lying orbits. However, this classification does not apply to hard radiation generated without the participation of nuclei and atoms.
X-ray fluxes are formed during the deceleration of charged fast particles (protons, electrons, and others) and due to processes that occur inside atomic electron shells. Gamma vibrations arise as a result of processes inside the nuclei of atoms and during the transformation of elementary particles.
Radio streams
Due to the large value of the lengths, these waves can be considered without taking into account the atomistic structure of the medium. As an exception, only the shortest streams, which are adjacent to the infrared region of the spectrum, act. In the radio range, the quantum properties of oscillations are manifested rather weakly. Nevertheless, they must be taken into account, for example, when analyzing the molecular standards of time and frequency while cooling the equipment to a temperature of several kelvins.
Quantum properties are also taken into account when describing generators and amplifiers of the millimeter and centimeter ranges. The radio stream is formed during the movement of alternating current through the conductors of the corresponding frequency. And a passing electromagnetic wave in space excites an alternating current corresponding to it. This property is used in the design of antennas in radio engineering.
Visible streams
Ultraviolet and infrared visible radiation in the broad sense of the word is the so-called optical portion of the spectrum. The selection of this area is determined not only by the proximity of the corresponding zones, but also by the similarity of the instruments used in the study and developed mainly during the study of visible light. These include, in particular, mirrors and lenses for focusing radiation, diffraction gratings, prisms, and others.
The frequencies of optical waves are comparable with those of molecules and atoms, and their lengths are with intermolecular distances and molecular sizes. Therefore, phenomena that are caused by the atomistic structure of matter become significant in this area. For the same reason, light, along with wave, has quantum properties.
The occurrence of optical streams
The most famous source is the sun. The surface of a star (photosphere) has a temperature of 6000 ° Kelvin and emits bright white light. The highest continuous spectrum is located in the green zone - 550 nm. There is also a maximum of visual sensitivity. Fluctuations in the optical range occur when the bodies are heated. Infrared fluxes are therefore also called thermal fluxes.
The stronger the heating of the body occurs, the higher the frequency where the maximum of the spectrum is located. With a certain increase in temperature, incandescence is observed (glow in the visible range). In this case, first red color appears, then yellow and further. The creation and registration of optical flows can occur in biological and chemical reactions, one of which is used in photography. For most creatures living on Earth, photosynthesis acts as a source of energy. This biological reaction occurs in plants under the influence of optical solar radiation.
Features of electromagnetic waves
The properties of the medium and the source influence the characteristics of the flows. This establishes, in particular, the temporal dependence of the fields, which determines the type of flow. For example, when changing the distance from the vibrator (with increasing), the radius of curvature becomes larger. The result is a plane electromagnetic wave. Interaction with matter also occurs in different ways.
The processes of absorption and radiation of flows, as a rule, can be described using classical electrodynamic relations. For waves in the optical region and for hard rays, their quantum nature should be taken into account all the more.
Stream sources
Despite the physical difference, everywhere - in a radioactive substance, a television transmitter, an incandescent lamp - electromagnetic waves are excited by electric charges that move with acceleration. There are two main types of sources: microscopic and macroscopic. First, there is an abrupt transition of charged particles from one to another level inside molecules or atoms.
Microscopic sources emit x-ray, gamma, ultraviolet, infrared, visible, and in some cases long-wave radiation. As an example of the latter, we can give the line of the spectrum of hydrogen, which corresponds to a wave of 21 cm. This phenomenon is of particular importance in radio astronomy.
Sources of the macroscopic type are emitters in which periodic synchronous oscillations are made by the free electrons of the conductors. In systems of this category, flows are generated from millimeter to the longest (in power lines).
Flow structure and strength
Electric charges moving with acceleration and periodically changing currents affect each other with certain forces. The direction and their magnitude depend on factors such as the size and configuration of the region in which currents and charges are contained, their relative direction and magnitude. The electrical characteristics of a particular medium, as well as changes in the concentration of charges and the distribution of currents of the source, also have a significant effect.
Due to the general complexity of the problem statement, it is impossible to present the law of forces in the form of a single formula. The structure, called the electromagnetic field and considered, if necessary, as a mathematical object, is determined by the distribution of charges and currents. It, in turn, is created by a given source when boundary conditions are taken into account. Conditions are determined by the shape of the interaction zone and the characteristics of the material. If we are talking about unlimited space, these circumstances are supplemented. In such cases, the radiation condition acts as a special additional condition. Due to it, the "correctness" of field behavior at infinity is guaranteed.
Study timeline
Lomonosov’s corpuscular-kinetic theory in some of its positions anticipates certain postulates of the electromagnetic field theory: the “rotary” (rotational) motion of particles, the “fluctuating” (wave) theory of light, its generality with the nature of electricity, etc. Infrared fluxes were discovered in 1800 year by Herschel (an English scientist), and the following year, 1801, ultraviolet was described by Ritter. Radiation of a shorter than ultraviolet range was discovered by X-ray in 1895, November 8. Subsequently, it was called x-ray.
The influence of electromagnetic waves has been studied by many scientists. However, the first to investigate the possibilities of flows, the scope of their application, was Narkevich-Iodko (Belarusian scientist). He studied the properties of flows as applied to practical medicine. Gamma radiation was discovered by Paul Willard in 1900. In the same period, Planck conducted theoretical studies of the properties of the black body. In the process of studying, he discovered the quantum nature of the process. His work was the beginning of the development of quantum physics. Subsequently, several works of Planck and Einstein were published. Their research led to the formation of such a concept as a photon. This, in turn, laid the foundation for the creation of a quantum theory of electromagnetic fluxes. Its development continued in the writings of leading scientists of the twentieth century.
Further research and work on the quantum theory of electromagnetic radiation and its interaction with matter led eventually to the formation of quantum electrodynamics in the form in which it exists today. Among the outstanding scientists who studied this issue, we should mention, in addition to Einstein and Planck, Bohr, Bose, Dirac, de Broglie, Heisenberg, Tomonaga, Schwinger, Feynman.
Conclusion
The importance of physics in the modern world is quite large. Almost everything that is used today in human life has appeared due to the practical use of the research of great scientists. The discovery of electromagnetic waves and their study, in particular, led to the creation of conventional, and subsequently mobile phones, radio transmitters. Of particular importance is the practical application of such theoretical knowledge in the field of medicine, industry, and technology.
Such widespread use is due to the quantitative nature of science. All physical experiments are based on measurements, comparing the properties of the studied phenomena with the available standards. For this purpose, within the framework of the discipline, a complex of measuring instruments and units is developed. A number of laws are common to all existing material systems. So, for example, the laws of conservation of energy are considered general physical laws.
In general, science is called fundamental in many cases. This is due, first of all, to the fact that other disciplines give descriptions, which, in turn, obey the laws of physics. So, in chemistry, atoms, substances formed from them, and transformations are studied. But the chemical properties of bodies are determined by the physical characteristics of molecules and atoms. These properties are described by such sections of physics as electromagnetism, thermodynamics, and others.