Download Unit 2 Electric Charge and Electric Field 1. Learn the following

Unit 2
Electric Charge and Electric Field
1. Learn the following words:
to conserve - сохранять
to manifest – делать
to depict - описывать
repulsive- отталкивающий
очевидным
to convergе - приближаться
to exert – оказывать
particles - частицы
to emanatе - происходить
давление
bound - предел
angle - угол
to suspend - прекращать
to diminishe - уменьшать
hollow - пустота
string - дополнительный
inverse - противоположный
scalar - скалярный
rod - рычаг
negligible - незначительный
slope - наклон
cloth - ткань
repulsion - отталкивание
irrelevant – не относящийся
to repel - отталкивать
arrow - указатель
к делу
2.Read and translate the text:
Electric Charge and Electric Field
Electric charge is a physical property of matter that causes it to experience a force when near other
electrically charged matter. Electric charge comes in two types, called positive and negative. Two
positively charged substances, or objects, experience a mutual repulsive force, as do two negatively
charged objects. Positively charged objects and negatively charged objects experience an attractive
force.
The Ancient Greek philosopher Thales of Miletus around 600 BC founded that charge (or electricity)
could be accumulated by rubbing fur on various substances, such as amber (the charged amber buttons
could attract light objects such as hair). And they noted that if they rubbed the amber for long enough,
they could even get a spark to jump.
The presence of charge gives rise to an electrostatic force: charges exert a force on each other, an effect
that was known, though not understood, in antiquity. A lightweight ball suspended from a string can be
charged by touching it with a glass rod that has itself been charged by rubbing with a cloth. If a similar
ball is charged by the same glass rod, it is found to repel the first: the charge acts to force the two balls
apart. Two balls that are charged with a rubbed amber rod also repel each other. However, if one ball is
charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other.
These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb,
who deduced that charge manifests itself in two opposing forms. So for the first time an electric charge
was introduced in Coulomb's law in 1785. The unit of measurement of the charge «SI» - Coulombelectric charge passing through the cross section of the conductor when a current of 1A for a time of 1s.
Charge in one very large Coulomb. If two of the charge carrier (q1=q2 =1C) arranged in a vacuum at a
distance of 1m, they would have interacted with the power of 9×109 H, that is with the force with which
the Earth's gravity would have attracted an object with a mass of about 1 million tons. This discovery led
to the well-known axiom: like-charged objects repel and opposite-charged objects attract. So, same-sign
charged particles repel one another, while different-sign charged particles attract. This is expressed
quantitatively in Coulomb's law, which states the magnitude of the repelling force is proportional to the
product of the two charges, and weakens proportionately to the square of the distance. The amount of
charge is usually given the symbol Q and expressed in coulombs; each electron carries the same charge
of approximately −1.6022×10−19 coulomb. The proton has a charge that is equal and opposite, and thus
+1.6022×10−19 coulomb.
The electric charge of a macroscopic object is the sum of the electric charges of its constituent particles.
Often, the net electric charge is zero, since naturally the number of electrons in every atom is equal to
the number of the protons, so their charges cancel out. Situations in which the net charge is non-zero
are often referred to as static electricity. Furthermore, even when the net charge is zero, it can be
distributed non-uniformly (e.g., due to an external electric field), and then the material is said to be
polarized, and the charge related to the polarization is known as bound charge (while the excess charge
brought from outside is called free charge). An ordered motion of charged particles in a particular
direction (in metals, these are the electrons) is known as electric current. The discrete nature of electric
charge was proposed by Michael Faraday in his electrolysis experiments, then directly demonstrated by
Robert Millikan in his oil-drop experiment.
Formally, a measure of charge should be a multiple of the elementary charge e (charge is quantized),
but since it is an average, macroscopic quantity, many orders of magnitude larger than a single
elementary charge, it can effectively take on any real value. Furthermore, in some contexts it is
meaningful to speak of fractions of a charge; e.g. in the charging of a capacitor.
The total electric charge of an isolated system remains constant regardless of changes within the system
itself.
The electric charge is a fundamental conserved property of some subatomic particles, which determines
their electromagnetic interaction. Electric charge is usually denoted by the letters q andQ. Electrically
charged matter is influenced by, and produces, electromagnetic fields. The interaction between a
moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of
the four fundamental forces. This is also evident the fundamental difference between the
electromagnetic forces of gravity. Gravitational forces are always forces of attraction.
An electric charge brought near one or more other electric charges will experience an electrical force.
One of the fundamental laws of electricity is that like charges (either positive or negative) repel each
other, and unlike charges attract each other. The region in which a charge experiences an electrical
force is called an electric field.
Electric field
According to modern concepts, the electric charges do not affect each other directly. Each charged body
creates in the surrounding electric field. This field exerts a force action on other charged bodies. The
main property of the electric field - effect on the electrical charges with a certain force. Thus, the
interaction of charged bodies is carried out not by direct their influence on each other, and through the
electric field surrounding the charged body.
An electric field can be regarded as the sphere of influence of an electrically charged object. Anything
that has an electrical charge will affect, and be affected by, other charged bodies. If two charged objects
are placed sufficiently close to one another, each will experience a measureable force acting upon it.
The field is theoretically infinite in extent, but its magnitude diminishes with distance from the source
according to the inverse square law. This means that if the distance is doubled, the strength of the field
is divided by four, and at three times the distance, the strength is divided by nine, and so on; the field
therefore becomes negligible at large distances.
An electric field is created by a charged body in the space that surrounds it, and results in a force
exerted on any other charges placed within the field. The electric field acts between two charges in a
similar manner to the way that the gravitational field acts between two masses, and like it, extends
towards infinity and shows an inverse square relationship with distance. However, there is an important
difference. Gravity always acts in attraction, drawing two masses together, while the electric field can
result in either attraction or repulsion.
The electric field is a vector field, which means that it has a direction as well as a magnitude. The force
experienced by a charged object in an electric field can be calculated as F = Eq, where F is the force in
Newtons, E is the electric field in volts per meter (v/m) and q is the charge in Coulombs.
An electric field line can be drawn with an arrow pointing away from a positive charge and pointing
toward a negative charge. Thus, a positively charged object would be depicted with field lines pointing
away from it in all directions, and a negatively charged object with field lines converging upon it. This,
however, is just a convention and does not indicate that there is anything physical pointing in a
particular direction.
The study of electric fields created by stationary charges is called electrostatics. The field may be
visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This
concept was introduced by Faraday, whose term 'lines of force' still sometimes sees use. The field lines
are the paths that a point positive charge would seek to make as it was forced to move within the field;
they are however an imaginary concept with no physical existence, and the field permeates all the
intervening space between the lines. Field lines emanating from stationary charges have several key
properties: first, that they originate at positive charges and terminate at negative charges; second, that
they must enter any good conductor at right angles, and third, that they may never cross nor close in on
themselves.
A hollow conducting body carries all its charge on its outer surface. The field is therefore zero at all
places inside the body. This is the operating principal of the Faraday cage, a conducting metal shell
which isolates its interior from outside electrical effects.
Electric potential
Electric potential - is the work done by the field forces on a single charge moving from one field to the
point of infinity.
The concept of electric potential is closely linked to that of the electric field. A small charge placed
within an electric field experiences a force, and to have brought that charge to that point against the
force requires work. The electric potential at any point is defined as the energy required to bring a unit
test charge from an infinite distance slowly to that point. It is usually measured in volts, and one volt is
the potential for which one joule of work must be expended to bring a charge of one coulomb from
infinity. This definition of potential, while formal, has little practical application, and a more useful
concept is that of electric potential difference, and is the energy required to move a unit charge
between two specified points. An electric field has the special property that it is conservative, which
means that the path taken by the test charge is irrelevant: all paths between two specified points
expend the same energy, and thus a unique value for potential difference may be stated. The volt is so
strongly identified as the unit of choice for measurement and description of electric potential difference
that the term voltage sees greater everyday usage.
For practical purposes, it is useful to define a common reference point to which potentials may be
expressed and compared. While this could be at infinity, a much more useful reference is the Earth
itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the
name earth or ground. Earth is assumed to be an infinite source of equal amounts of positive and
negative charge, and is therefore electrically uncharged—and unchargeable.
Electric potential - time component of the four-dimensional electromagnetic potential, sometimes also
called the scalar potential (scalar - in three-dimensional sense, Lorentz invariant of the group, he is not,
then there is not the same when you change the frame of reference). After the electric potential φ
expressed by the electric field strength:
where
- gradient operator (nabla), and A - the vector potential, which is expressed through the (also)
a magnetic field. In the particular case of constant or negligibly slow time-varying electric and magnetic
fields (the case of electrostatics), the electric potential is called the electrostatic potential, and the
formula for the electric field (referred to in this case, electrostatic) is simplified, since the second term of
(derivative time) is equal to zero (or sufficiently small as compared with the first - and may be equal to
zero within the approximation):
In this case, it is not difficult to see, is lost (missing) vortex electric field, Field E - potentially, and hence
should be able to determine the electrostatic E potential through the work done by the electric field, as
it is in this case is completely determined by the potential difference in the initial and final point
The electric field was formally defined as the force exerted per unit charge, but the concept of potential
allows for a more useful and equivalent definition: the electric field is the local gradient of the electric
potential. Usually expressed in volts per metre, the vector direction of the field is the line of greatest
slope of potential, and where the equipotentials lie closest together.
Adapted from:http://www.physics.ru/courses/op25part2/content/chapter1/section/paragraph2/theory.html#.Vz3
http://physics.ru/courses/op25part2/content/chapter1/section/paragraph1/theory.html#.Vz3-ljdv601
http://bourabai.ru/toe/voltage.htm https//en.wikipedia.org/wiki/ Electricity
-FTdv600
3. Give the Russian equivalents for the following English words and phrases:
to experience a force, a mutual repulsive force, an attractive force, a fundamental conserved property
of some subatomic particles, electromagnetic interaction, could be accumulated by rubbing fur on
various substances, get a spark to jump, charges exert a force on each other, like-charged objects repel,
opposite-charged objects attract, same-sign charged particles repel one another, while different-sign
charged particles attract, expressed quantitatively in Coulomb's law, is proportional to the product of
the two charges, weakens proportionately to the square of the distance, the number of electrons in
every atom is equal to the number of the protons, bound charge, oil-drop experiment, infinite in extent,
magnitude diminishes, the inverse square law, becomes negligible at large distances, an arrow pointing,
may be visualised by a set of imaginary lines, emanating from stationary charges, they originate at
positive charges and terminate at negative charges; they must enter any good conductor at right angles,
they may never cross nor close in on themselves, a hollow conducting body, electric potential, to be an
infinite source of equal amounts of positive and negative charge, a scalar quantity, the equipotentials
cross all lines, at right angles, the force exerted per unit charge, in volts per metre, the line of greatest
slope of potential.
4. Give the English equivalents for the following Russian words and phrases:
сила притяжения, испытывать, взаимный, электромагнетическое влияние, искра, заряженные
частицы, закон Кулона, обратно пропорционально, бесконечное пространство, значительное
уменьшение, становиться незначительным, происходить от неподвижных электрических зарядов,
завершаться, под углом,служить проводником, напряжение, положительные и отрицательные
заряды, вызывать напряжение.
5. Answer the questions:
1. What is electric charge?
2. What is the source of the electromagnetic force?
3. What did Thales of Miletus found around 600 BC?
4. What phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb?
5.Who proposed the discrete nature of electric?
6. How can an electric field be regarded?
7. Why does the field become negligible at large distances?
8. What did Michael Faradaye introduce?
9.What is the definition of potential?
6. Speak on:
- Like-charged objects repel and opposite-charged objects attract.
- The concept of the electric field was introduced by Michael Faraday.
- Electrostatics.
- Electric potential.
7. Read and speak on:
Static electricity
Charge carriers, particularly electrons, can build up or become deficient on objects without flowing
anywhere. You’ve experienced this when walking on a carpeted floor during the winter or in a place
where the humidity is low. An excess or shortage of electrons is created on and in your body. You
acquire a charge of static electricity. It’s called static because it doesn’t go anywhere. You don’t feel this
until you touch some metallic object that is connected to an electrical ground or to some large fixture,
but then there is a discharge, accompanied by a spark and a small electric shock.
When the atoms that make up an object lose or gain electrons, the object acquires a net electric charge.
An object with a positive charge tends to attract electrons; one with a negative charge tends to repel
them.
Static electricity exists when an object has a net electric charge and there is no movement of electrons
into or away from the object. Part or all of a static charge is lost when the charged object touches an
uncharged or oppositely charged object.
Objects that carry the same electric charge, caused by either an excess or a deficiency of electrons, repel
each other. If you were massively charged, the spark might jump several centimeters. Such a charge is
dangerous. Static electric (also called electrostatic) charge build up of this magnitude does not happen
with ordinary carpet and shoes, fortunately. However, a device called a Van de Graaff generator, found
in some high-school physics labs, can cause a spark this large. You have to be careful when using this
device for physics experiments. On the grand scale of the Earth’s atmosphere, lightning occurs between
clouds and between clouds and the surface. This spark is a greatly magnified version of the little spark
you get after shuffling around on a carpet. Until the spark occurs, there is an electrostatic charge in the
clouds, between different clouds, or between parts of a cloud and the ground. The direction of the
current flow in these cases is considered to be the same as the direction in which the electrons move. In
cloud-to-ground or ground-to-cloud lightning, the charge on the Earth’s surface follows along beneath
the thunderstorm cloud like a shadow as the storm is blown along by the prevailing winds. The current
in a lightning stroke can approach 1 million A. However, it takes place only for a fraction of a second.
Still, many coulombs of charge are displaced in a single bolt of lightning.
Application
- Dust removal: There are some appliances that can eliminate dust from the air, like air purifiers. They
use static electricity to alter the charges in the dust particles so that they stick to a plate or filter of the
purifier that has an opposite charge as that of the dust (opposite charges attract each other). This effect
is also used in industrial smokestacks to reduce the pollution that they generate, altough they work in a
very large scale, the effect is basically the same as the home air purifier.
- Photocopy: Copy machines use static to make ink get attracted to the areas where we need the
information copied. It uses the charges to apply the ink only in the areas where the paper to be copied is
darker (usually this means text or other information) and not where the paper is white, this process is
called xerography.
- Car painting: To make sure a car's paint is uniform and that it will resist the high speeds and weather
to protect the car's metal interior, it is applied with a static charge. The metal body of the car is
submerged in a substance that charges it positively, and the paint is charged negatively with the paint
sprayer. This process ensures a uniform layer of paint, since when there is enough negative paint in the
car the extra will be repelled by the paint already in the car. It also ensures that the paint won't fall off,
since the electrical attraction between the paint and the car is stronger than if it was just sprayed.
- Power from Static Electricity?
Many people have wondered if static electricity can be used as a source of power for homes and
industries. Despite the extremely high voltages that can be generated with static electricity (tens of
thousands of volts, compared that to the 110v of a common power outlet) the amount current it can
generate is very low, from microAmperes to a few miliAmperes (Ampere is the unit of electric current)
and only for very short times. Lightning can produce a considerable amount of energy, but the high
voltages, current, temperature and speed of the discharge make it extremely difficult and inefficient to
use or store Adapted from: Hobart Mason - Static Electricity//Harvard University//Department of Engineering
http://newchemistry.ru/letter.php?n_id=1484
8.Give the Russian translation of the text:
Статическое электричество возникает, когда у объекта имеется избыток электронов, или когда у
объекта имеется недостаток электронов. У объектов с избытком электронов имеется
отрицательные (-) заряд, а у объектов с недостатком электронов положительный (+) заряд. Такое
отсутствие электронного баланса создает нестабильное энергетическое состояние. Таким
образом, заряженные объекты стремятся к нейтрализации для того, чтобы выйти из этого
нестабильного энергетического состояния. В результате, электроны идут по пути наименьшего
сопротивления для заземления или уходят в атмосферу для создания равновесия зарядов
объекта. Такой электронный разряд называется электростатическим разрядом. Наиболее
предсказуемой характеристикой электростатического разряда является то, что он направляется
для заземления по пути наименьшего сопротивления; тем не менее, время прохождения такого
разряда совершенно непредсказуемо. Именно эта непредсказуемость электростатического
разряда и затрудняет контроль отказов компонентов и съедает доходы электронных компаний.
Время прохождения разряда зависит от типа материала, который разряжается. Проводники
разряжаются очень быстро. Материалы, рассеивающие энергию, разряжаются за считанные
секунды. Изолирующие материалы, напротив, могут не разряжаться от нескольких минут до
нескольких часов.
9. Read and discuss:
Electrical phenomena in nature
Electricity is not a human invention, and may be observed in several forms in nature, a prominent
manifestation of which is lightning. Many interactions familiar at the macroscopic level, such as touch,
friction or chemical bonding, are due to interactions between electric fields on the atomic scale. The
Earth's magnetic field is thought to arise from a natural dynamo of circulating currents in the planet's
core. Certain crystals, such as quartz, or even sugar, generate a potential difference across their faces
when subjected to external pressure. This phenomenon is known as piezoelectricity, from the Greek
piezein (πιέζειν), meaning to press, and was discovered in 1880 by Pierre and Jacques Curie. The effect is
reciprocal, and when a piezoelectric material is subjected to an electric field, a small change in physical
dimensions takes place.
Some organisms, such as sharks, are able to detect and respond to changes in electric fields, an ability
known as electroreception, while others, termed electrogenic, are able to generate voltages themselves
to serve as a predatory or defensive weapon. The order Gymnotiformes, of which the best known
example is the electric eel, detect or stun their prey via high voltages generated from modified muscle
cells called electrocytes. All animals transmit information along their cell membranes with voltage pulses
called action potentials, whose functions include communication by the nervous system between
neurons and muscles An electric shock stimulates this system, and causes muscles to contract. Action
potentials are also responsible for coordinating activities in certain plants.
Adapted from:https//en.wikipedia.org/wiki/ Electricity