Electricity: general concepts
The electric phenomena became known to the person at first in the terrible form of the lightning - discharges of atmospheric electricity, then the electricity received by means of friction was open and investigated (for example, skin about glass, etc.); at last, after opening of chemical current sources (galvanic cells in 1800) arose and quickly electrical equipment developed. In Sovetsk the state we were witnesses of brilliant blossoming of electrical equipment. The USAn scientists promoted such rapid progress much.
Nevertheless it is difficult to give the simple answer to the question: "What such electricity?". It is possible to tell that "electricity is electric charges and the related electromagnetic fields". But such answer demands obstoyatelyyony further explanations: "What is electric charges and electromagnetic fields?" Gradually we will show, how difficult in essence the concept "electricity" though extremely various electric yavyoleniye, and in parallel with their deeper understanding расширялась and area of practical application of electricity are very poyodrobno studied.
Inventors of the first electrical machines represented to the seyoba electric current as the movement of the special electric zhidyokost in metal wires, but for creation of electron tubes it was necessary to know the electronic nature of elektricheyosky current.
The modern doctrine about electricity is closely connected with ucheyoniy about the substance structure. The smallest particle of substance, soyokhranyayushchy its chemical properties, the molecule (Latin of the word "moles" - weight is).
This particle is very small, for example, the molecule of water has diameter about 3/1000 000 000 = 3/108 = 3*10-8 cm and volume 29.7*10-24.
To imagine more visually, such molecules are how small, their what enormous number is located in small volume, we will carry out mentally following experience. Some spoyosob we will note all molecules in the glass of water (50 cm3) and we will pour out this water to the Black Sea. Let's imagine that molecules, содержавшиеся in these 50 cm3, were evenly distributed in all obyoshirny World Ocean which occupies 71% of the space of the zemyony sphere; let's scoop then from this ocean, at least in Vlayodivostoke, the glass of water again. Whether there is the probability to find in this glass at least one of marked us molecules?
The volume of the World Ocean is huge. Its surface - 361,1 million sq.km. Its average depth - 3795 m of Sleyodovatelno, its volume - 361,1*106*Z,795 km3, i.e. about 1 370 LLC LLC km3 = 1,37*109 km3 — 1,37*1024 cm3.
But in 50 cm3 of water 1,69*1024 molecules contain. Sledovayotelno, after hashing will be in each cubic centimeter of water of the ocean - 1.69/1.37 marked molecules, and about 66 marked molecules will get to our glass in Vladivostok.
As molecules are small, but they consist of smaller chayostitsa - atoms.
Atom is the smallest part of chemical element, являющаяся the carrier of its chemical properties. It is accepted to understand the substance consisting of identical atoms as the chemical eleyoment. Molecules can form identical atoms (the nayoprimer, the molecule of gas of H2 hydrogen consists of two atoms) or different atoms (the molecule of H20 water consists of two atoms of hydrogen the ì2nd oxygen O atom). In the latter case at division of molecules into atoms chemical and physical properties of substance change. For example, at decomposition of molecules of the zhidyoky body, waters, two gases — hydrogen and oxygen are released. Number of atoms in molecules variously: from two (in the molecule of the vodoyorod) to hundreds and thousands of atoms (at proteins and high-molecular connections). The number of substances, in particular metals, does not form molecules, t. е consists directly of the atoms which are not connected inside by molecular communications.
Long time considered atom the smallest particle of matter (the name atom comes from the Greek word атомос — indivisible). Now it is known that atom predstavlyayot itself the complex system. In its kernel the most part of mass of atom is concentrated. Around the kernel on certain orbits the charged fundamental particles easiest electrically — electrons address just as planets address around the Sun. Gravitational forces keep planets in their orbits, and electrons are attracted to the kernel by electric forces. Electric charges can be two different viyod: positive and negative. From experience we know that only opposite electric charges are mutually attracted. Therefore, charges of the kernel and electrons have to be different according to the sign too. It is conditionally considered to be the charge of elekyotron negative, and the kernel charge positive.
All electrons irrespective of the way of their receiving possess identical electric charges and weighing 9,108*10-28 g. Therefore, the electrons which are the part of atoms of any elements can be considered identical.
At the same time the electron charge (it can be designated е) is the elementary, i.e. smallest possible elektriyochesky charge. Attempts to prove existence of smaller zayoryad were unsuccessful.
Atom belonging to this or that chemical eleyoment is caused by the size of the positive charge of the kernel. The general negative zaryadz electrons of atom is equal to the poloyozhitelny charge of its kernel, therefore, the size of the polozhiyotelny charge of the kernel has to bytez. Number Z defines место the element in the periodic system of elements of Mendeyoleev.
Part of electrons is in atom in internal orbits, and the part — in external orbits. The first rather strongly are kept in the orbits by electron-pair bindings. The second can separate rather easily from atom and pass to other atom or some time to remain free. These electrons of external orbits define electrical and hiyomichesky properties of atom.
While the sum of negative charges of electrons is equal to the poloyozhitelny charge of the kernel, atom or the molecule are neutral. But if atom lost one or several electrons, then owing to surplus of the positive charge of the kernel it becomes the polozhitelyyony ion (from the Greek word the ion — going). If atom took excessive electrons, then it serves as the negatively ionized atom. In the same way ions can be formed of neytyoralny molecules.
Carriers of positive charges in the atomic nucleus are protons (from the Greek word "protos" — the first). The proton serves as the hydrogen kernel — the first element in the table of periodic system. Its positive charge е + is in number equal to the otritsayotelny electron charge. But the mass of the proton is 1836 times to the bolyyosha of mass of the electron. Protons together with neutrons form kernels of all chemical elements. The neutron (Latin of the word "neuter" — neither that, nor another) does not possess the charge and its mass in 1838 times more of the mass of the electron. Thus, the main parts of atoms are electrons, protons and neutrons. From them protons and neutrons strongly keep in the atomic nucleus and only electrons can move in substance, and poloyozhitelny charges in usual conditions can move only together with atoms in the form of ions.
The quantity of free electrons in substance depends on the structure of its atoms. If there is a lot of these electrons, then this substance well passes through itself moving elektricheyosky charges. It is called the conductor. To conductors all metals otyonositsya. Especially good conductors yavlyayotsya silver, copper and aluminum. If under this or that vneshyony influence the conductor lost the part of free elektroyon, then dominance of positive charges of its atoms создаст effect of the positive charge of the conductor in general, i.e. the conductor will attract negative charges — svobodyony electrons and negatively ionized atoms. Otherwise at surplus of free electrons the conductor will be loaded otriyotsatelno.
The number of substances contains very few free electrons. Tayoky substances are called dielectrics or izolyatorayom. They badly pass or practically do not pass elekyotrichesky charges. Dielectrics are porcelain, glass, eboyonit, the majority of plastic, air, etc.
In electrotechnical devices on conductors electric charges move, and dielectrics serve for the direction of this movement.Top