Early history of electricity
History shows us that at least 2500 year ago, or so, the Greeks were already familiar with the strange force(as is seemed to them) which is known today as electricity. Generally speaking, three phenomena made up all of man’s knowledge of electrical effects. The first phenomenon under consideration was the familiar lighting flash – a dangerous power, as it seemed to them, which could both kill people and burn or destroy their houses. The second manifestation of electricity he was more or less familiar with was the following: he sometimes found in the earth a strange yellow stone which looked like glass. On being rubbed, that strange yellow stone, that is to say amber, obtained the ability of attracting light objects of a small size. The third was connected with the so-called electric fish which possessed the property of giving more or less strong electric shocks which could be obtained by a person coming into contact with the electric fish.
Nobody knew that the above phenomena were due to electricity. People could neither understand their observations nor find any practical applications for them.
As a matter of fact, all of man’s knowledge in the field of electricity has been obtained during the last 370 years, or so. Needless to say, it took a long time before scientists learned how to make use of electricity. In effect, most of the electrically operated devices, such as the electric lamp, the refrigerator, the tram, the lift, the radio, and so on, are less than one hundred years old.
In spite of their having been employed for such a short period of time, they play a most important part in man’s everyday life all over the world. In fact, we cannot do without them at present.
We have not named the scientists who contributed to the scientific research on electricity as centuries passed. However, famous names are connected with its history and among them we find that of Phales, the Greek philosopher. As early as about 600 B.C. (that is, before our era) he discovered that when amber was rubbed, it attracted and held for some time light objects. However, he could not know that amber was charged with electricity owing to the process of rubbing. Then Gilbert, the English physicist, began the first systematic scientific research on electrical phenomena. He discovered that various other substances possessed the property similar to that of amber or, in other words, they generated electricity when they were rubbed. He gave the name “electricity” to the phenomenon he was studying. He got this word from the Greek “electrum” meaning “amber”.
Many learned men of Europe began to use the new word “electricity” in their conversation as they were engaged in research of their own. Scientists of the Russia, France and Italy made their contribution as well as the Englishmen and the Germans.
Electric current serves us in a thousand ways
The electric current was born in the year 1800 when Volta constructed the first source of continuous current. Since that time numerous scientists and inventors, Russian and foreign, have greatly contributed to its development and practical application.
As a result, we cannot imagine modern civilization without the electric current. We can’t imagine how people could do without electric lamps, without vacuum cleaners, refrigerators, washing machines and other electrically operated devices that are widely used today. In fact, telephones, lifts, electric trams and trains, radio and television have been made possible only owing to the electric current.
Many people are more familiar with the various applications of the electric current in their everyday life than they are with its numerous industrial applications. However, electric energy finds its most important use in industry. Take, for example, the electric motor transforming electric energy into mechanical energy. It finds wide application at every mill and factory. As for the electric crane, it can easily lift objects weighing hundreds of tons.
A good example which is illustrating an important industrial use of the electric current is the electrically heated furnace. Great masses of metal melted in such furnaces flow like water. Speaking of the melted metals, we might mention one more device using electricity that is the electric pyrometer. The temperature of hot flowing metals can be easily measured owing to the electric pyrometer.
These are only some of the various industrial applications of the electric current serving us in a thousand ways.
Electric current
Ever since Volta first produced a source of continuous current, men of science have been forming theories on this subject. For some time they could see no real difference between the newly-discovered phenomenon and the former understanding of static charges. Then the famous French scientist Ampere (after whom the unit of current was named) determined the difference between the current and the static charges. In addition to it, Ampere gave the current direction: he supposed the current to flow from the positive pole of the source round the circuit and back again to the negative pole.
We consider Ampere to be right in his first statement but he was certainly wrong in the second, as to the direction of the current.
Let us turn our attention now to the electric current itself. The current which flows along wires consist of moving electrons. What can we say about the electron? We know the electron to be a minute particle having an electric charge. We also know that that charge is negative. As these minute charges travel along a wire, that wire is said to carry an electric current.
In addition to traveling through solids, however, the electric current can flow though liquids as well and even through gases. In both cases it produces some of most important effects to meet industrial.
Some liquids, such as melted metals for example, conduct current without any change to themselves. Other, called electrolytes are found to change greatly when the current passes through them.
When the electrons flow in one direction only, the current is known to be d.c., that is, direct current. The simplest source of power for the direct current is a battery, for a battery pushes the electrons in the same direction all the time (i.e., from the negatively charged terminal to the positively charged terminal).
The letters a.c. stand for alternating current. The current under consideration flows first is one direction and then in the opposite one. The a.c. used for power and lighting purposes is assumed to go through 50 cycles in one second. One of the great advantages of a.c. is the ease with which power at low voltage can be changed into an almost similar amount of power at high voltage and vise versa. Hence, on the one hand alternating voltage is increased when it is necessary for long-distance transmission and, on the other hand, one can decrease it to meet industrial requirements as well as to operate various devices at home.
Although there are numerous cases when d.c. is required, at least 90 per cent of electrical energy to be generated at present at is a.c. In fact, it finds wide application for lighting, heating, industrial and some other purposes.
Electric circuit
The electric circuit is the subject to be dealt with in the present article. But what does that above term really mean? We know the circuit to be a complete path which carries the current from the source of supply to the load and then carriers it again from the load back to the source.
The purpose of the electrical source is to produce the necessary electromotive force required for the flow of current through the circuit.
The path along which the electrons travel must be complete otherwise no electric power can be supplied from the source to the load. Thus we close the circuit when we switch on our electric lamp.
If the circuit is broken or, as we generally say “opened’ anywhere, the current is known to stop everywhere. Hence, we break the circuit when we switch off our electrical devices. Generally speaking, the current may pass through solid conductors, liquids, gases, vacuum, or any combination of these. It may flow in turn over transmission lines from the power-stations through transformers, cables and switches, through lamps, heaters, motors and so on.
There are various kinds of electric circuits such as: open circuits, closed circuits, series circuits, parallel circuits and short circuits.
To understand the difference between the following circuit connections is not difficult at all. When electrical devices are connected so that the current flows from one device to another, they are said to be connected in series. Under such conditions the current flow is the same in all parts of the circuit, as there is only a single path along which it may flow. The electrical bell circuit is considered to be a typical example of a series circuit. The parallel circuit provided two or more paths for the passage of current. The circuit is divided in such a way that part of the current flows through one path, and part through another. The lamps in your room and your houses are generally connected in parallel.
Now we shall turn our attention to the short circuit sometimes called “the short”. The short circuit is produced when the current is allowed to return to the source of supply without control and without doing the work that we want it to do. The short circuit often results from cable fault or wire fault. Under certain conditions, the short may cause fire because the current flows where it was not supposed to flow. If the current flow is too great a fuse is to be used as a safety device to stop the current flow.
The fuse must be placed in every circuit where there is a danger of overloading the line. Then all the current to be sent will pass through the fuse.
When a short circuit or an overload causes more current to flow than the carrying capacity of the wire, the wire becomes hot and sets fire to the insulation. If the flow of current is greater than the carrying capacity of the fuse, the fuse melts and opens the circuit.
Generators
The dynamo invented by Faraday in 1831 is certainly a primitive apparatus compared with the powerful, highly efficient generators and alternators that are in use today. Nevertheless, these machines operate on the same principle as the one invented by the great English scientist. When asked what use his new invention had, Faraday asked in his turn: “What is the use of new-born child?” As a matter of fact, “the new-born child” soon became an irreplaceable device we cannot do without.
Although used to operate certain devices requiring small currents for their operation, batteries and cells are unlikely to supply light, heat and power on a large scale. Indeed, we need electricity to light up millions of lamps, to run trains, to lift things and to drive the machines. Batteries could not supply electricity enough to do all this work.
That dynamo-electric machines are used for this purpose is a well-known fact. These are the machines by means of which mechanical energy is turned directly into electrical energy with a loss of only a few per cent. It is calculated that they produce more than 99.99 per cent of all the world’s electric power.
There are two types of dynamos, namely, the generator and the alternator. The former supplies d.c. which is similar to the current from a battery and the latter, as its name implies provides a.c.
To generate electricity both of them must be continuously provided with energy from some outside source of mechanical energy such as steam engines, steam turbines or water turbines, for example.
Both generators and alternators consist of the following principal parts: an armature and an electromagnet. The electromagnet of a d.c. generator is usually called a stator which located in a static condition while the armature (the rotor) is rotating.
Alternators may be divided into two types: 1. alternators that have a stationary armature and a rotating electromagnet; 2. alternators whose armature serves as a rotor but this is seldom done. In order to get a strong e.m.f. the rotors in large machines rotate at a speed of thousands of revolutions per minute (r.p.m.). The faster they rotate, the grater the output voltage the machine will produce.
In order to produce electricity under the most economical conditions, the generators must be as large as possible. In addition to it, they should be kept as fully loaded as possible all the time.
above – выше
advantage – преимущество, выгода
allow – позволять
almost – почти
along – по всей линии
alternating – переменный
alternator – альтернатор
amount – количество, доходить
application – применение
armature – якорь
article – статья, параграф
assume – принимать на себя
assumed – допускаемый, предполагаемый
cables – кабель
capacity – вместимость, емкость, объем, объем
carrier – несущий
carry – переносить
case – случай
cell – элемент,
charge – заряд, ответственность
combination – сочетание, комбинация
complete – полный, совершенный
conduct – поведение
consider – рассматривать, обсуждать
consideration – рассмотрение, обсуждение
conversation – разговор, беседа
crane – грузоподъемный кран
dealt – распределять, иметь дело
decrease – уменьшение
device – устройство
direct current – прямой ток
direction – руководство, управление, направление
due – обусловленный
electric pyrometer – электрический пирометр
electrolyte – электролит
electromotive force – электродвижущая сила
employ – использовать, нанимать, держать на службе
familiar – близкий, хорошо знакомый
fault – дефект, недостаток
flow – течение, поток
found – плавиться
furnace – печь, очаг, топка
fuse – плавка, плавиться (Эл. плавкий предохранитель)
generally – главным образом.
generator – генератор
greatly – очень, значительно
hand – передавать
heat – жар, теплота, накаливать
heater – радиатор, нагревательный прибор
hence – следовательно
hold – захватывать
imply – заключать в себе, подразумевать, значить
indeed – в самом деле
irreplaceable – незаменимый
latter – недавний, последний
lift – поднятие, подъем, подъемник, лифт
liquids – жидкий
load – нагрузка
loss – потеря, утрата, пропажа, убыток
manifestation – проявление
matter – предмет (обсуждения)
measure – измерять, мерить, мерка
mechanical – машинный, механический
melt – таять, плавиться, расплавленный металл, плавка
mill – фабрика, завод
minute – мелкий, мельчайший
motor – двигатель, мотор
needless – ненужный, лишний, бесполезный
negative – отрицательный
operate – работать, эксплуатировать, управлять
opposite – напротив, противоположность
order – порядок
otherwise – иначе
output – производительность, емкость, мощность
owing – обязанный
particle – частица
passes – двигаться вперед
path – траектория, линия действия
pole – полюс
power-stations – электростанция
power-house – электростанция
provide – снабжать, заготовлять
purpose – намерение, цель
push – толкать ускорять, выпускать
require – требовать
required – необходимый
requirements – нужда, потребность, требование
rub – трение
same – один и тот же, одинаковый
seem – казаться, представляться
series – последовательное соединение
similar – подобный
solids – твердое тело
source – источник
statement – утверждение, заявление
supply – снабжать
supposed – мнимый, предполагаемый, предполагал
term – выражать, называть, термин
terminal – клемма
thus – таким образом
transform – превращать, преображать
transmission – передача, передаточный
turn – вращаться, вертеться
vacuum – вакуумный, вакуум
vise versa – переменное напряжение
voltage – напряжение
weigh – весить, взвешиваться
wide – широкий, большой, далекий
wires – проволока
wrong – неправда, вредить