Electricity, set of the phenomena caused by existence, the movement and interaction electrically of the electrified bodies or particles. Interaction of electric charges is carried out by means of the electromagnetic field (in case of motionless electric charges - electrostatic field).
Moving charges (electric current) along with electric excite also magnetic field, i.e. generate the electromagnetic field by means of which electromagnetic interaction is carried out (the doctrine about magnetism is the constituent of the general doctrine about electricity). The electromagnetic phenomena are described by classical electrodynamics which cornerstone the equations are Maxwell
Laws of the classical theory of electricity cover huge set of electromagnetic processes. Among 4 types of the interactions (electromagnetic, gravitational, strong and weak) existing in the nature electromagnetic win first place on the width and the variety of manifestations. It is connected with the fact that all bodies are constructed of electrically charged particles of opposite signs, interactions between which, on the one hand, on many orders more intensively gravitational and weak, and with another - are long-range unlike strong couplings. The structure of atomic covers, coupling of atoms in molecules (chemical forces) and formation of the condensed substance are defined by electromagnetic interaction.
The simplest electric and magnetic phenomena are known from the extreme antiquity. The minerals attracting iron pieces were found and also it is revealed that the amber (the Greek electron, elektron, from here the term electricity) rubbed about wool attracts easy subjects (triboelectrification). However only in 1600 U. Gilbert for the first time established difference between the electric and magnetic phenomena. It opened existence of magnetic poles and their inseparability from each other and also established that the globe - the huge magnet.
In XVII - the 1st half of the 18th centuries numerous experiments with electrified bodies were made, the first electrostatic machines based on triboelectrification were constructed, existence of electric charges of two childbirth is established (Sh. Dyufa), the conductivity of metals (the English scientist S. Gray) is found. With the invention of the first condenser - the Leyden jar (1745) - there was the opportunity to accumulate big electric charges. In 1747-53 Franklin stated the first consecutive theory of the electric phenomena, finalized the electric nature of the lightning and invented the lightning arrester.
In the 2nd half of the 18th century quantitative studying of the electric and magnetic phenomena began. There were first measuring apparatuses - electroscopes of different designs, electrometers. G. Cavendish (1773) and Highway. The Coulomb (1785) experimentally established the law of interaction of motionless point electric charges (Cavendish's works were published only in 1879).
This fundamental law of the electrostatics (The Coulomb the law) for the first time allowed to create the method of measurement of electric charges on forces of interaction between them. The Coulomb established also the law of interaction between poles of long magnets and entered the concept about the magnetic charges concentrated on the ends of magnets.
The following stage in advancement of science about electricity is connected with opening at the end of the 18th century by L. Galvani of "animal electricity" and works And. Volts which invented the first source of electric current - the galvanic cell (the so-called voltaic column, 1800) creating continuous (constant) current for a long time. In 1802 V.V. Petrov, having constructed the galvanic cell of considerably bigger power, opened the electric arc, investigated its properties and pointed to the possibility of applications it for lighting and also for melting and welding of metals. G. Davy electrolysis of water solutions of alkalis received (1807) metals unknown earlier - sodium and potassium. J, P. Dzhoul established (1841) that the quantity of heat, allocated in the conductor by electric current, in proportion to the current intensity square; this law was proved (1842) by exact experiments E.H. Lenz (Joule-Lenz law).
G. The ohm established (1826) quantitative dependence of electric current on tension in the chain. K.F. Gauss formulated (1830) the main theorem of the electrostatics.
The most fundamental opening was made by H. Ersted in 1820; he found action of electric current on the magnetic needle - the phenomenon demonstrating communication between electricity and magnetism. After this the same year A.M. Ampere established the law of interaction of electric currents (Ampere the law). It showed also that properties of permanent magnets can be explained on the basis of the assumption that in molecules of the magnetized bodies direct electric currents (molecular currents) circulate. Thus, according to Ampere, all magnetic phenomena come down to interactions of currents, magnetic charges do not exist. Since opening of the Oersted and Ampere the doctrine about magnetism became the doctrine constituent about electricity.
Fast penetration of electricity into the equipment began with the 2nd quarter of the 19th century. In the 20th the first electromagnets appeared. The telegraph was one of the first use of electricity, in the 30-40th electric motors and generators of current, and in the 40th - electric lighting devices, etc. are constructed. Practical application of electricity more and more increased further that in turn rendered essential, influence on the doctrine about electricity.
In the 30-40th of the 19th century M. Faraday - the creator of the general doctrine about the electromagnetic phenomena in which all electric and magnetic phenomena are considered from the uniform point of view brought the big contribution in advancement of science about electricity. By means of experiences he proved that actions of electric charges and currents do not depend on the way of their receiving [to Faraday distinguished "ordinary" (received at triboelectrification), atmospheric, "galvanic", magnetic, thermoelectric, "animal" and other types E.].
In 1831 Faraday opened electromagnetic induction - excitation of electric current in the contour which is in the alternating magnetic field. This phenomenon (observed in 1832 also by J. Henry) makes the base of electrical equipment. In 1833-34 Faraday established laws of electrolysis; these its works laid the foundation for electrochemistry. Further it, trying to find interrelation of the electric and magnetic phenomena with optical, opened polarization of dielectrics (1837), the phenomena of paramagnetism and diamagnetism (1845), magnetic rotation of the plane of polarization of light (1845), etc.
Faraday introduced idea of electric and magnetic fields for the first time. He denied the concept of long-range action which supporters considered that bodies directly (through emptiness) act on distance at each other.
According to Faraday's ideas, interaction between charges and currents is carried out by means of intermediate agents: charges and currents create in surrounding space electric or (respectively) magnetic weeding through which interaction is transmitted from the point to the point (the concept of short-range interaction). At the heart of its ideas of electric and magnetic fields the concept of power lines which he considered as mechanical educations in the hypothetical environment - air, similar to the stretched elastic threads or cords lay.
Faraday's ideas about reality of the electromagnetic field gained recognition not at once. The first mathematical statement of Faraday laws of induction was given ф. Neumann in 1845 in language of the concept of long-range action.
It entered important concepts of coefficients most and interinductions of currents. The value of these concepts completely revealed later when U. Thomson (lord Calvin) developed (1853) the theory of electric fluctuations in the contour consisting of the condenser (electric capacitance) and coils (inductance).
Creation of new devices and methods of electric measurements and also the uniform system of electric and magnetic units of measurements created by Gauss and V. Weber was of great importance for development of the doctrine about electricity.
In 1846 Weber pointed to communication of current intensity with density of electric charges in the conductor and the speed of their ordered movement. He established also the law of interaction of moving point charges which contained the new universal electrodynamic constant representing the relation of electrostatic and electromagnetic units of the charge and dimensional speeds.
At experimental definition (Weber and t. Kolraush, 1856) this constant received the value close to light speed; it was the certain instruction on communication of the electromagnetic phenomena with optical.
In 1861-73 the doctrine about electricity gained the development and end in J.K. Maxwell's works. Being guided by empirical laws of the electromagnetic phenomena and having entered the hypothesis of generation of magnetic field variation electric field, Maxwell formulated the fundamental equations of classical electrodynamics called by his name. At the same time he, like Faraday, considered the electromagnetic phenomena as some form of mechanical processes on air.
The main new investigation following from these equations - existence of the electromagnetic waves extending with light speed. Maxwell equations formed the basis of the electromagnetic theory of light. Maxwell's theory found decisive confirmation in 1886-89 when G. Gerts experimentally established existence of electromagnetic waves. After its opening attempts to establish connection with the help of electromagnetic waves, come to the end with creation of radio were made, and intensive researches in the field of radio engineering began.
At the end of XIX - the beginning of the 20th centuries the new stage in development of the theory of electricity began. Researches of electric discharges crowned discovery of discretization of electric charges by J.J. Thomson. In 1897 it measured the electron charge relation to its weight, and in 1898 defined the absolute value of the electron charge. H. Lorentz, relying on Thomson's opening and conclusions of the molecular and kinetic theory, laid the foundation of the electronic theory of the structure of substance. In the classical electronic theory substance is considered as set electrically of the charged particles which movement is subordinated to laws of classical mechanics. Maxwell equations turn out from the equations of the electronic theory statistical averaging.
Attempts of application of laws of classical electrodynamics to the research of electromagnetic processes in moving environments encountered essential difficulties. Aiming to resolve them, A. Einstein came (1905) to relativity of the theory. This theory finally disproved the idea of existence of air allocated with mechanical properties. After creation of theory of relativity it became obvious that laws of electrodynamics cannot be consolidated to laws of classical mechanics.
On small spatio-temporal intervals there are essential quantum properties of the electromagnetic field which are not considered by the classical theory of electricity. The quantum theory of electromagnetic processes - quantum electrodynamics - was created in the 2nd quarter of the 20th century. The quantum theory of substance and the field already goes beyond the doctrine about electricity, studies more fundamental problems concerning laws of the movement of fundamental particles and their structure.
With opening of the new facts and creation of new theories the value of the classical doctrine about electricity did not decrease, only limits of applicability of classical electrodynamics were defined. In these limits of Maxwell equation and the classical electronic theory remain in force, being the base of the modern theory of electricity.
Classical electrodynamics makes the basis of the majority of sections of electrical equipment, radio engineering, electronics and optics (the exception the quantum electronics makes). By means of its equations the huge number of problems of theoretical and applied character was solved. In particular, numerous problems of behavior of plasma in vitro and in space are solved by means of Maxwell equations.Top