Download Electric current

Unit 3
Electric current
1. Learn the following words:
hole - дыра
multiples – многочисленный (кратный)
conventional – стандартный (условный)
storage – накопление (аккумулятор)
portable – портативный
stroke – удар (ход вверх или вниз)
to bolt - скреплять
to prong – протыкать
to plug - затыкать
conversely - обратно
lethal - фатальный
pump - насос
to dissipatе - рассеивать
consequence - последствие
collisions - столкновение
impuritу - примесь
clay - глина
utility - практичный
to jar – вибрировать (дребезжать)
store - запас
layer - слой
foils - следы
to coil – обматывать
decay - распад
to inducе - индуктировать
inductance -индуктивность
to equalize – уравнивать
resistance - сопротивление
2.Read and translate the text:
Electric current
Electric current is electric charge in motion. It can take the form of a sudden discharge of static
electricity, such as a lightning bolt or a spark between your finger and a ground light switch plate.
More commonly, though, when we speak of electric current, we mean the more controlled form
of electricity from generators, batteries, solar cells or fuel cells. Most electric charge is carried by
the electrons and protons within an atom. Protons have positive charge, while electrons have
negative charge. However, protons are mostly immobilized inside atomic nuclei, so the job of
carrying charge from one place to another is handled by electrons. Electrons in a conducting
material such as a metal are largely free to move from one atom to another along their conduction
bands, which are the highest electron orbits.
Electric current, any movement of electric charge carriers, such as subatomic charged particles
(e.g., electrons having negative charge, protons having positive charge), ions (atoms that have lost
or gained one or more electrons), or holes (electron deficiencies that may be thought of as positive
particles).
Electric current in a wire, where the charge carriers are electrons, is a measure of the quantity of
charge passing any point of the wire per unit of time. In alternating current (q.v.) the motion of the
electric charges is periodically reversed; in direct current (q.v.) it is not. In many contexts the
direction of the current in electric circuits is taken as the direction of positive charge flow, the
direction opposite to the actual electron drift. When so defined the current is called conventional
current.
Current in gases and liquids generally consists of a flow of positive ions in one direction together
with a flow of negative ions in the opposite direction. To treat the overall effect of the current, its
direction is usually taken to be that of the positive charge carrier. A current of negative charge
moving in the opposite direction is equivalent to a positive charge of the same magnitude moving
in the conventional direction and must be included as a contribution to the total current. Current
in semiconductors consists of the motion of holes in the conventional direction and electrons in
the opposite direction.
Electric current generates an accompanying magnetic field. When an electric current flows in an
external magnetic field, it experiences a magnetic force, as in electric motors. The heat loss, or
energy dissipated, by electric current in a conductor is proportional to the square of the current.
A common unit of electric current is the ampere, a flow of one coulomb of charge per second, or
6.2 × 1018 electrons per second. The centimetre–gram–second units of current are either
the electrostatic unit of charge (esu) per second or the absolute electromagnetic unit (abamp). One
abamp equals 10 amps; 1 amp equals 3 × 109 esu per second.
Commercial power lines make available about 100 amps to a typical home; a lightbulb pulls about
1 amp of current and a one-room air conditioner about 15 amps.
Current = Flow of Electrons
Calculating Current
•
•
•
I – current (Amperes A or C/s)
Q – total charge (C)
∆t – time (s)
Q
𝐼=
∆t
An electric current exists when there is a net flow of electrically charged particles. Most uses of
electricity involve the flow of electrons. Some electric currents, such as those that occur in a
battery, involve the flow of positive and negative ions. (By convention, the direction of a current
in an electric circuit is considered to be the direction in which positive charge would flow, and is
opposite the direction of electron flow.) An electric current has energy that can be converted to
heat or light, or—as in an electric motor—used to perform mechanical work.
So, there are two basic types of electric current—direct current (DC) and alternating current (AC).
In a direct current, the direction of the flow of electric charge does not change, although the current
may increase and decrease. Alternating current, in contrast, regularly reverses direction.
The electric current delivered to the home from an electric power company is alternating current.
Its main advantage is that its voltage (electrical pressure) can be easily increased or decreased (by
devices called transformers). Another advantage is that AC machinery is generally simpler to
design and build than DC machinery. Direct current, however, is needed by electronic devices and
for such processes as charging storage batteries and electroplating. An advantage of direct current
is that it can be readily produced by batteries for use in portable devices.
Current can flow only if it gets a “push.” This push can be provided by a build up of electrostatic
charges, as in the case of a lightning stroke. When the charge builds up, with positive polarity
(shortage of electrons) in one place and negative polarity (excess of electrons) in another place, a
powerful Ohm’s law. If the emf is doubled, the current is doubled. If the resistance is doubled, the
current is cut in half. This law of electricity will be covered in detail a little later. It is possible to
have an emf without having current flow. This is the case just before a lightning bolt occurs and
before you touch a metallic object after walking on the carpet. It is also true between the two
prongs of a lamp plug when the lamp switch is turned off. It is true of a dry cell when there is
nothing connected to it. There is no current, but a current can flow if there is a conductive path
between the two points. Even a large emf might not drive much current through a conductor or
resistance. A good example is your body after walking around on the carpet. Although the voltage
seems deadly in terms of numbers (thousands), not many coulombs of charge normally can
accumulate on an object the size of your body. Therefore, not many electrons flow through your
finger, in relative terms, when you touch the metallic object. Thus you don’t get a severe shock.
Conversely, if there are plenty of coulombs available, a moderate voltage, such as 117 V (or even
less), can result in a lethal flow of current. This is why it is dangerous to repair an electrical device
with the power on. The utility power source can pump an unlimited number of coulombs of charge
through your body if you are foolish enough to get caught in this kind of situation.
The components in an electric circuit can take many forms, which can include elements such as
resistors, capacitors, switches, transformers and electronics.
The resistor is perhaps the simplest of passive circuit elements: as its name suggests, it resists the
current through it, dissipating its energy as heat. The resistance is a consequence of the motion of
charge through a conductor: in metals, for example, resistance is primarily due to collisions
between electrons and ions. Ohm's law is a basic law of circuit theory, stating that the current
passing through a resistance is directly proportional to the potential difference across it. The
resistance of most materials is relatively constant over a range of temperatures and currents;
materials under these conditions are known as 'ohmic'. The ohm, the unit of resistance, was named
in honour of Georg Ohm, and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will
produce a potential difference of one volt in response to a current of one amp. Some substances,
such as carbon, conduct electricity fairly well but not very well. The conductivity can be changed
by adding impurities such as clay to a carbon paste. Electrical components made in this way are
called resistors. They are important in electronic circuits because they allow for
the control of current flow. The better a resistor conducts, the lower is its resistance; the worse it
conducts, the higher is the resistance. Electrical resistance is measured in ohms, sometimes
symbolized by the upper case Greek letter omega. The higher the value in ohms, the greater is the
resistance, and the more difficult it is for current to flow. In an electrical system, it is usually
desirable to have as low a resistance, or ohmic value, as possible because resistance converts
electrical energy into heat. This heat is called resistance loss and in most cases represents energy
wasted.Thick wires and high voltages reduce the resistance loss in long-distance electrical lines.
This is why gigantic towers, with dangerous voltages, are employed in large utility systems.
The capacitor is a development of the Leyden jar and is a device that can store charge, and thereby
storing electrical energy in the resulting field. It consists of two conducting plates separated by a
thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the
surface area per unit volume and therefore the capacitance. The unit of capacitance is the farad,
named after Michael Faraday, and given the symbol F: one farad is the capacitance that develops
a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected
to a voltage supply initially causes a current as it accumulates charge; this current will however
decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit
a steady state current, but instead blocks it.
The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in
response to the current through it. When the current changes, the magnetic field does too, inducing
a voltage between the ends of the conductor. The induced voltage is proportional to the time rate
of change of the current. The constant of proportionality is termed the inductance. The unit of
inductance is the henry, named after Joseph Henry, a contemporary of Faraday. One henry is the
inductance that will induce a potential difference of one volt if the current through it changes at a
rate of one ampere per second. The inductor's behaviour is in some regards converse to that of the
capacitor: it will freely allow an unchanging current, but opposes a rapidly changing one. . An
electrical conductor is a substance in which the electrons are highly mobile. The best conductor,
at least among common materials, at room temperature is pure elemental silver. Copper and
aluminum are also excellent electrical conductors. Iron, steel, and various other metals are fair to
good conductors of electricity. Some liquids are good conductors. Mercury is one example. Salt
water is a fair conductor. Gases are, in general, poor conductors because the atoms or molecules
are too far apart to allow a free exchange of electrons. However, if a gas becomes ionized, it can
be a fair conductor of electricity. Electrons in a conductor do not move in a steady stream like
molecules of water through a garden hose. They pass from atom to atom. This happens to countless
atoms all the time. As a result, trillions of electrons pass a given point each second in a typical
electric circuit. In an electrical conductor, electrons pass easily
from atom to atom.
An electrical insulator prevent electric currents from flowing, except in very small amounts under
certain circumstances. Most gases are good electrical insulators (because they are poor
conductors). Glass, dry wood, paper, and plastics are other examples. Pure water is a good
electrical insulator, although it conducts some current when minerals are dissolved in it. Metal
oxides can be good insulators, even though the metal in pure form is a good conductor. An
insulating material is sometimes called a dielectric. This term arises from the fact that it keeps
electric charges apart, preventing the flow of electrons that would equalize a charge difference
between two places. Excellent insulating materials can be used to advantage in certain electrical
components such as capacitors, where it is important that electrons not be able to flow steadily.
When there are two separate regions of electric charge having opposite polarity (called plus and
minus, positive and negative) that are close to each other but kept apart by an insulating material,
that pair of charges is called an electric dipole.
Adaptedfrom:https://www.youtube.com/watch?v=8xONZcBJh5A
https://www.fxyz.ru/формулы_по_физике/электричество;
fizika.narod.ru/68_0.htm
http://pskgu.ru/ebooks/zsm_2/zs2_gl07_32.pdf ; http://files.schoolcollection.edu.ru/dlrstore/1f18f9a4-11f2-62fc-c906ea962b5c0aa2/1001197A.htm; http://studopedia.org/7-59656.html
http://nika-
3. Give the Russian equivalents for the folloving English words and phrases:
charged particles, a unit negative charge, a unit positive charge, charge carriers, a net flow of
electrically charged particles, can be converted to heat or light, used to perform mechanical work,
direct current (DC), alternating current (AC), electrical pressure, charging storage batteries,
electroplating, portable devices, a lightning stroke, shortage of electrons, excess of electrons, to
have an emf, a lightning bolt, a severe shock, dissipating its energy as heat, ohmic value, resistance
loss, large utility systems, the Leyden jar, can store charge, a thin insulating dielectric layer, thin
metal foils are coiled together, decay in time as the capacitor fills, a
4. Give the English equivalents for the folloving Russian words and phrases:
заряженные частицы, несущий (о токе), тепло и свет, механическая работа, поток
электронов,
проводник,
проводить
электричество,
аккумуляторная
батарея,
гальванопокрытие, световой удар,недостаток и избыток, сильный шок,оценка,
сопротивление, запас электрических зарядов, способность к насыщению.
5. Answer the questions:
1. What is electric current?
2. What can current consist of?
3. When does an electric current exist?
4.What are basic types of electric current?
5. What is Ohm’s law?
6. Why it is dangerous to repair an electrical device with the power on?
7. What is a resistor?
8. What is a capacitor?
9. What is an inductor?
6. Speak on:
- The electric current delivered to the home from an electric power company is alternating current.
- Ohm’s law.
- Current can flow if…
- Resistors.
- An electrical conductor.
- An electrical insulator.
7. Read and speak on:
Electronics
Electronics, the branch of science and technology concerned with the nature, uses, and
manufacture of devices in which electrons flow through a gas, vacuum, or semiconductor. All
electronic devices are electrical—that is, they use or produce electric energy. Electronic devices
are unique in that the flow of electricity in them can be controlled by electrical rather than
mechanical means. Examples of electronic devices include diodes, transistors, and X-ray tubes.
The early history of electronics is closely tied to experimentation with the Crookes tube, a type of
vacuum tube developed by Sir William Crookes, an English physicist and chemist. While
performing experiments with a Crookes tube, Wilhelm Konrad Roentgen, a German physicist,
discovered X rays in 1895. In 1897, Ferdinand Braun, another Germany physicist modified the
Crookes tube to make the first oscilloscope, an instrument that produces a visual image of an
electric signal.
Interest in improving the reception of radio waves led to the invention of the vacuum-tube diode
in 1904 by Sir John Fleming, an English electrical engineer, and to the invention of the vacuumtube triode in 1907 by Lee De Forest, a United States inventor. The invention of the triode was a
key event in the history of electronics, since it was the first electronic amplifier.
During World War I there was an increased interest in developing radio and electronics, and by
1920 the development of vacuum tubes and circuits employing them had advanced to the point
where their superiority over all other devices used in radio transmitters and receivers was apparent.
Regular commercial radio broadcasting in the United States began in 1920, and the demand for
household receivers soon made electronics an important industry.
Certain technical limitations in the operation of electron tubes were overcome with the
development of the pentode in 1929. The advances being made at this time helped lead to the
development of television; the first regular television broadcasting began in 1936, in London.
During World War II, emphasis was placed on the development of electronics for military use.
Radar was greatly improved and in 1944 the first large electronic digital computer, ENIAC, was
built. The main purpose of the computer was to speed up the calculation of tables of data for aiming
artillery. The electronics industry emerged from the war as a major industry. Its growth following
the war continued as television manufacturing entered a boom period and military programs
demanded more advanced electronic technology.
In 1948 William Shockley, John Bardeen, and Walter H. Brattain of Bell Telephone Laboratories
developed the first transistor, a forerunner of the bipolar junction transistor. During the early 1950's
the technology was developed to mass-produce transistors. The advantage of semiconductor
devices over electron tubes created a demand for techniques to further reduce the amount of space
required for electronic components. An important step toward miniaturizing electronic
components was the introduction of the integrated circuit in the early 1960's. The techniques
necessary to fabricate such circuits were pioneered by Jack Kilby of Texas Instruments in 1959.
During the 1970's and 1980's the size of the components of integrated circuits continued to be
reduced and the number of components that could be produced on each chip grew rapidly. With
increasing miniaturization, the capabilities of the electronic circuits and the speed at which they
could perform their functions greatly increased. Each advance helped reduce the cost of producing
electronic products.
Through the 1980's and into the 1990's, the variety of products being built with electronic
components increased, and the use of electronic control devices led to greater automation.
Microelectronics led to the development of new technologies, such as digital audio recording; to
the introduction of new products, such as personal computers; and to the reduction in the size of
portable telephones and many other electronic products.
In most nonelectronic devices, electricity supplies energy for such purposes as heating or lighting,
or running electric motors. In most electronic devices, electricity is used to represent and convey
some type of information. The information may be simple, such as an indication that the door of
an automobile is open, or it may be complex, such as the sounds produced by a group of musical
instruments. The changes in voltage or current that are used to represent information are called
electrical signals.
An analog electronic device works with continuously varying electrical signals. These signals are
typically used to represent quantities that vary continuously. For example, the radio waves used in
AM radio have continuously varying amplitudes that represent the varying pitch and loudness of
a sound, and television signals have continuously varying frequencies to represent the varying
patterns of brightness and darkness of a scene.
A digital electronic device works with sequences of pulse-like signals. These signals are coded
to represent numbers, making them especially useful for operations that require numerical
calculations, as in a digital computer. In many digital electronic devices, a series of numerical
values can be used to represent a continuously varying quantity. For example, the sound recorded
on an audio compact disc is recorded digitally.
The representation of the way an electric current or voltage varies with time is called a waveform.
Analog signals generally have smoothly varying waveforms called sine waves. Digital signals
generally have rectangular waveforms, rising and falling abruptly between two levels.
In general, electronic systems are designed to detect various kinds of signals. They then modify
these signals or produce new signals based on the signals they detect. For example, a compact disc
player detects the variations in the light reflected from the surface of a rotating disc. Using this
information, it produces an electric current that re-creates the sound by means of earphones or
loudspeakers.
One of the most important functions performed by electronic systems is the strengthening, or
amplification, of weak signals. In a sound system, for example, a compact disc player produces
only a weak signal; through amplification, the system can produce the much stronger signals
required by earphones or loudspeakers.
Other important functions carried out by electronic systems include rectification, the conversion
of an alternating current to a direct current; oscillation, the production of various kinds of regular
waveforms from a direct current; and switching operations called logic functions.
Active components in turn are divided into two fundamental groups: (1) semiconductor, or solidstate, devices; and (2) electron tubes.
There are several ways of defining a semiconductor. Historically, the term semiconductor has been
used to denote materials with a much higher conductivity than insulators, but a much lower
conductivity than metals measured at room temperature. Today there are two more types of
conductors: superconductors and semiconductors and insulators. This definition is not complete.
What really distinguishes metals from semiconductors is the temperature dependence of the
conductivity. While metals (except for superconductors) and semimetals retain their metallic
conductivity even at low temperatures, semiconductors are transformed into insulators at very low
temperatures. In this sense semiconductors and insulators are actually one class of materials, which
differs from metals and semimetals, which from another class. This classification is directly
connected to the existence of a gap between occupied and empty states, i.e., an energy gap, in
semiconductors and insulators.
The operation of semiconductor devices depends on the behavior of electrons in a semiconductor,
a material whose ability to conduct electricity is between that of a conductor and that of an
insulator. Most electronic devices in use today are semiconductor devices. The operation of
electron tubes depends on the behavior of electrons moving through a vacuum or gas inside a
closed container.
An electron tube is essentially a sealed hollow enclosure in which the movement of electrons can
be carefully controlled. The enclosure is typically made of glass and contains various metal parts
called electrodes for producing and regulating a beam of electrons.
An electron tube from which all gases have been removed is called a vacuum tube. In most types
of vacuum tubes, one of the electrodes must be heated to emit electrons. (This emission is called
thermionic emission.) The most important types of vacuum tubes are the cathode-ray tube and the
X-ray tube. Such vacuum tubes as the triode, the pentode, and the vacuum-tube diode were once
important, but they have been almost entirely replaced by comparable semiconductor devices that
are smaller and more durable. In addition, vacuum tubes consume much more electric energy than
semiconductor devices because they require electrical heating for thermionic emission.
Adapted from:http://lingualeo.com/ru/jungle/electronics-and-microelectronics-48272#/page/3
8.Give the Russian translation of the text:
Электроника (от греч. Ηλεκτρόνιο — электрон) — наука о взаимодействии
электронов с электромагнитными полями и методах создания электронных приборов и
устройств для преобразования электромагнитной энергии, в основном для приёма,
передачи, обработки и хранения информации.
История
Возникновению
электроники
предшествовало
изобретение радио.
Поскольку
радиопередатчики сразу же нашли применение (в первую очередь на кораблях и в военном
деле), для них потребовалась элементная база, созданием и изучением которой и занялась
электроника. Элементная база первого поколения была основана на электронных лампах.
Соответственно получила развитие вакуумная электроника. Её развитию способствовало
также изобретение телевидения и радаров, которые нашли широкое применение во
время Второй мировой войны.
Но электронные лампы обладали существенными недостатками. Это прежде всего большие
размеры и высокая потребляемая мощность (что было критичным для переносных
устройств). Поэтому начала развиваться твердотельная электроника, а в качестве
элементной базы стали применять диоды и транзисторы.
Дальнейшее развитие электроники связано с появлением компьютеров. Компьютеры,
основанные на транзисторах, отличались большими размерами и потребляемой
мощностью, а также низкой надежностью (из-за большого количества деталей). Для
решения этих проблем начали применяться микросборки, а затем и микросхемы. Число
элементов микросхем постепенно увеличивалось, стали появляться микропроцессоры. В
настоящее время развитию электроники способствует появление сотовой связи, а также
различных беспроводных устройств, навигаторов, коммуникаторов, планшетов и т. п.
Основными вехами в развитии электроники можно считать:
 изобретения А. С. Поповым радио (7
мая 1895
года),
и
начало
использования радиоприёмников,
 изобретение Ли де Форестом лампового триода, первого усилительного элемента,
 использование Лосевым полупроводникового элемента для усиления и генерации
электрических сигналов,
 развитие твердотельной электроники,
 использование
проводниковых
и
полупроводниковых
элементов
(работы Иоффе, Шотки),
 изобретение в 1947 году транзистора (Уильям Шокли, Джон Бардин и Уолтер
Браттейн),
 создание интегральной микросхемы и последующее развитие микроэлектроники,
основной области современной электроники.
9. Read and discuss:
Physiological effects
A voltage applied to a human body causes an electric current through the tissues, and although the
relationship is non-linear, the greater the voltage, the greater the current. The threshold for
perception varies with the supply frequency and with the path of the current, but is about 0.1 mA
to 1 mA for mains-frequency electricity, though a current as low as a microamp can be detected
as an electrovibration effect under certain conditions. If the current is sufficiently high, it will
cause muscle contraction, fibrillation of the heart, and tissue burns. The lack of any visible sign
that a conductor is electrified makes electricity a particular hazard. The pain caused by an electric
shock can be intense, leading electricity at times to be employed as a method of torture. Death
caused by an electric shock is referred to as electrocution. Electrocution is still the means of
judicial execution in some jurisdictions, though its use has become rarer in recent times.
Cultural perception
In 1850, William Gladstone asked the scientist Michael Faraday why electricity was valuable.
Faraday answered, “One day sir, you may tax it.”
In the 19th and early 20th century, electricity was not part of the everyday life of many people,
even in the industrialised Western world. The popular culture of the time accordingly often depicts
it as a mysterious, quasi-magical force that can slay the living, revive the dead or otherwise bend
the laws of nature. This attitude began with the 1771 experiments of Luigi Galvani in which the
legs of dead frogs were shown to twitch on application of animal electricity. "Revitalization" or
resuscitation of apparently dead or drowned persons was reported in the medical literature shortly
after Galvani's work. These results were known to Mary Shelley when she authored Frankenstein
(1819), although she does not name the method of revitalization of the monster. The revitalization
of monsters with electricity later became a stock theme in horror films.
As the public familiarity with electricity as the lifeblood of the Second Industrial Revolution grew,
its wielders were more often cast in a positive light, such as the workers who "finger death at their
gloves' end as they piece and repiece the living wires" in Rudyard Kipling's 1907 poem Sons of
Martha. Electrically powered vehicles of every sort featured large in adventure stories such as
those of Jules Verne and the Tom Swift books. The masters of electricity, whether fictional or
real—including scientists such as Thomas Edison, Charles Steinmetz or Nikola Tesla—were
popularly conceived of as having wizard-like powers.
With electricity ceasing to be a novelty and becoming a necessity of everyday life in the later half
of the 20th century, it required particular attention by popular culture only when it stops flowing,
an event that usually signals disaster. The people who keep it flowing, such as the nameless hero
of Jimmy Webb’s song "Wichita Lineman" (1968), are still often cast as heroic, wizard-like
figures.
Adapted from:
https//en.wikipedia.org/wiki/ Electricity