Download electricity

UNIT 6
ELECTRICITY
Vocabulary:




Electricity
Magnetism
Electromagnetism
Generators and transformers
Grammar:


Integrated practice of grammar structures and functions
Revision of connectors
LISTENING:
ELECTRICITY
Electricity is a phenomenon of SOME CHARGED SUBATOMIC PARTICLES called
electrons WHEN THEY START MOVING FROM ATOM TO ATOM. An atom is the smallest
particle OF WHICH ALL MATTER IS COMPOSED. All atoms consist of a nucleus
CONTAINING PROTONS AND NEUTRONS, AROUND WHICH ELECTRONS ORBIT; in fact,
electrons orbiting farther from the nucleus ARE MORE EASILY DRAWN AWAY and
therefore are more likely to move and CREATE AN ELECTRIC CURRENT
The different particles that make up an atom carry different electric charges; thus, AN
ELECTRON IS NEGATIVELY CHARGED whereas a proton is positively charged and
NEUTRONS HAVE NO ELECTRICAL CHARGES. Under normal conditions an atom is
electrically neutral AS THERE ARE AS MANY PROTONS AS ELECTRONS IN ONE ATOM.
However atoms of different substances DIFFER FROM EACH OTHER DEPENDING ON
THE NUMBER OF ELECTRONS AND PROTONS that they contain.
IN SPITE OF THE FACT THAT THE NUCLEUS IS THE SMALLEST PART OF AN
ATOM, most of the atom’s weight is concentrated in its nucleus. A proton and a neutron
each weigh approximately 1 atomic weight unit. An electron, ON THE OTHER HAND,
weighs only about 1/1800 (one eighteen hundredth) OF THE WEIGHT OF A PROTON OR
NEUTRON
Yet to produce the movement of electrons A DIFFERENCE IN POTENTIAL BETWEEN
TWO POINTS must be created. Electric sources SUCH AS BATTERIES, CELLS,
GENERATORS, etc change chemical, mechanical or other types of energy INTO
ELECTRICAL ENERGY
77
CONNECTORS
1. Electrons are very light –WHEREAS/WHILE-- protons and neutrons have most of
the mass of the atom.
2. –INSTEAD OF-- using the common metric units, the amstrong is preferred to
measure atoms. Common metric units are not widely used to measure atoms; the
amstrong is preferred INSTEAD
3. Electrons orbiting farther from the nucleus move to other atoms –DUE TO THE
FACT THAT/SINCE--they are more easily drawn away.
4. Unlike charges attract each other; THUS/THEREFORE/HENCE/THEREBY , a
positively charged atom will attract electrons from other atoms.
5. Electricity occurs DUE TO the movement of electrons.
6. –IN SPITE OF/DESPITE--the nucleus being the smallest part of an atom, it contains
most of its mass.
7. Electrons, protons and neutrons are called subatomic particles SINCE/DUE TO THE
FACT THAT they are smaller than an atom.
8. ALTHOUGH/WHEREAS-- the structure of atoms is similar for all elements, each
element has a different number of electrons protons and neutrons.
9. The new submarine could not take human beings to the deepest parts of the ocean.
It carried lots of cameras and photographic equipment INSTEAD--.
10. The new alloy they have just created is very expensive, but it is NEVERTHELESS-extremely resistant to pitting and rusting… YET it is extremely resistant to pitting
and rusting
11. Research is underway to obtain superconducting properties at room temperature,
WHICH-- is quite interesting for the field of telecommunications.
12. The robot should get to the third sector, IN WHICH/WHERE -- there is a serious
power shortage. ALTHOUGH
13. The failure has certainly appeared –DUE TO-- low quality fuel.
14. All cables are coated with a special material, (---THUS---) protecting the whole
circuit.
15. –DUE TO THE FACT THAT/SINCE- we do not have pictures from the area, we have
to believe what its inhabitants tell us. ALTHOUGH
READING: ELECTROMAGNETISM
The generation of large amounts of electricity has been possible thanks to relationship that
exists between electricity and magnetism. Magnetism is a property that occurs naturally in certain
substances, especially iron with small amounts of carbon, and can be transferred to or induced in
others. It consists of attracting and repelling other materials, and some materials can be magnetised
quite easily just by placing them in contact with a permanent magnet.
The force of magnetism is dipolar; thus, a magnet always has two poles, namely North and
South which are located at the ends of the magnet. When two magnets are placed side by side, like
poles will repel each other whereas unlike poles will attract due to the forces of attraction and
repulsion created between both magnets.
The area around a magnet where the magnetic forces are
exhibited is called the magnetic field, represented by the lines of force.
77
The lines of force indicate the strength and direction of the magnetic field; the ends of a magnet
contain more lines of force and as a consequence of this, the field is stronger there. In addition, the
lines of force always run from North to South and this phenomenon creates the attraction or repulsion
between two magnets.
In the 19th century, scientists like Hans Oersted, Faraday or Ampere made discoveries about
the relationship between electricity and magnetism. It was found that the forces between magnetic
dipoles are identical to those between electrical dipoles and that electrical currents generate a
magnetic field. Oersted discovered accidentally that the electric current possessed the property of
magnetism. He had left a compass on the table where he was experimenting with an electric current.
(A compass is a navigational device with a magnetised needle which points to the earth’s North and
South magnetic poles). Oersted observed that the needle moved whenever the current was turned
on, attracted by the magnetic field created around the wire. Further research
revealed that it was possible to generate an electric current in a conductor by
changing the magnetic fields around it, a phenomenon known as electromagnetism,
a discovery which has led to the development of many devices which make use of
electromagnetism, including electric motors, generators and transformers. Without
these devices, electricity could never have become a major source of power.
EXERCISES
A. Say whether these statements are TRUE or FALSE.
1- A magnet attracts mainly iron.
2- A piece of iron can be magnetised by adding carbon to it.
3- In a magnet, the north pole is negatively charged and the south pole is positively charged.
4- The north pole of the earth is attracted by the north pole of a magnet.
5- The lines of force run from the North pole to the South pole.
6- Hans Oersted discovered the relationship between electricity and magnetism by chance.
7- In a magnet, the needle points to the geographic North pole.
8- Nowadays most electric motors are based on the principle of electromagnetism.
B. Find nouns for these words in the text
ADDition
DIRECTion/or
STRONG/strength
DEVELOPment
ABLE/ability
ATTRACTion
SCIENCE/scientist
GENERATE/or-tion
MAGNETism
REPEL/repulsion (repellent)
DISCOVERy
TRANSFORMer/ation
VIDEO: MAGNETIC CIRCUITS (O.U.)
As you watch the video complete the following text. Fill in the dots with prepositions and
broken lines with expressions and concepts
77
This is the well-known display of ----------------------------of a permanent magnet displayed .... the
-----------of iron filings.
The whole of this programme is ..............displaying --------------------------in one way or another.
But, o f course the trouble with magnetic fields is that you cannot actually see them. So, what I've got
to try to do in this programme is to -----------------------them to you and to show -------------------------------- by showing their effects ................ the fields themselves.
This particular display of the---------------------------------- shows the field very clearly because the
iron filings distribute themselves ................ ----------------------------------------, if that's the ---------------and
that's the South pole, the ------------------------------------------------------------and the iron filings distribute
themselves ..........these lines pointing .................the pole pieces of the magnet. So in that particular
instance, the field is very clearly demonstrated.
I can represent this with a diagram. --------------------------------: N ........ one end and S. ..... the
other, and the lines of force are running ----------------------------, roughly along the same patterns as
you saw in the iron filings demonstration. So, this is ---------------------------------of the kind of thing that
happens with a permanent magnet.
Now, let's put two permanent magnets side .... side. ------------------------------------------you
get.
They're
squeezed
together
.............these two magnets, when the N is ..........N, and S. is .........S.
What does this actually mean -------------------------------?
I can show this with some actual permanent magnets that I
have here, ---------------------------------------, with N pole marked at each
end so that this resembles the diagram you just looked at. If I push the two together quite clearly -----------------------------------; if I press the two together side by side, it is firmly pushed away. So, --------------------------------------. So let's look back at the diagram to see how that might explain it.
You see here the lines are apparently compressed and they actually behave very much as
though they are -----------------------------------------------; so that when lines of force get compressed like
that, they do represent ------------------------------------------- shown here by these white arrows.
If I --------------------------------------------- so that N is now ---------------- S, I'm sure you are very
familiar with the fact they attract -------------------------- like this. This again can be shown ......... the
diagram. Here the ----------------------------now running .....N .... S are, so to speak, pulling the magnets
together and there's -----------------------------------------again shown by the arrows. That much I'm sure is
very familiar to you.
The first main point I want to get over is that actually -----------------------------------------------------------------------------------------to do this.
Here I've got some pieces of iron. They ------------------------------at all, they ----------------------------------------------, but if I put them along side these magnets like this, ............. one side so that the two
magnets face each other once again, the two N poles -------------------, the two N poles ..........each
other, so that the magnets should repel ------------------------, what do you think will happen?
Let's see. -------------------------------. The ----------------------------------------------has been almost
completely removed. So, what’s happened is that the ----------------------------- which was filling the gap
.........the magnets has been shunted away down the iron; --------------------------------------------------------route (…) for magnetic fields than does air; so it shunts it away and -------------------------------------------Let's have a look at this in the diagram.
Here you see the magnetic lines which were in the gap .................them as they are still
................... the gap, but now the lines have been shunted .............the iron represented .... this light
grey area, shunted through there, --------------------------------, in both magnets and the gap between
them, you see, has no lines of force left, -------------------------------------------------------------------either.
Now I can demonstrate this effect rather more dramatically with a different pair of magnets.
Here I have a ferrite magnet. --------------------------------, ceramic in nature and ----------------------------------quite strongly. Here you see there are two rings, one ......the other, the upper one is being
supported -----------------------exerted .....the lower one. All the magnetic forces interact to be more
77
exact. This kind of levitation of a body .......magnetic field will be demonstrated in the next television
programme where the method is used to levitate a train .........the track.
But I can show you how the field can be shunted away ..............these two by taking these
pieces of iron again and slipping them between the magnets. As I put them in, ---------------------------------until there isn't any left and the upper magnet sinks ............ onto the lower one, and -------------------------------------left; removing these pieces of iron restores the levitation of the ring magnet.
So shunting a magnetic field is an important ability that you can use to shape the magnetic
fields for more practical purposes. A more important use is guiding a magnetic field to the place you
want it.
PREPOSITIONS
FARADAY’S EXPERIMENT
This is a paragraph about one of Faraday´s experiments. Complete it by putting the
correct preposition from the list. You can use the same preposition more than once.
at
in
between
of
to
on
by
Let´s have a look __AT 1__ one of Faraday´s experiments, __IN 2 __ which he used
a copper wheel and a horseshoe magnet. The wheel was located __BETWEEN 3 __ the
poles __OF 4__ the magnet. Electrical contacts were applied __ TO 5__ the wheel, both
__IN/AT 6__ the centre and __ON/AT 7__ the edge of it. These parts were connected __
TO 8__ an ammeter __9 BY__ means of wires __10 IN__ order to detect the electrical
current. Whenever the wheel rotated __11 BETWEEN__ the ends of the magnet, an
electrical current was shown __ ON 12__ the ammeter´s display. When the wheel was
77
made to turn __ON/TO 13__ the opposite direction, the needle __OF 14__ the ammeter
was deflected __ON/TO 15__ the opposite direction, too. Therefore, according __ TO 16__
this experiment, the direction of the current depended __ON 17__ the turning of the
wheel placed close __TO 18__ a magnetic field.
77
TRANSLATION
ELECTROMAGNETISM
Some
SCIENTISTS
ELECTROMAGNETISM
WHO
(científicos
WORKED/(WHO
que
trabajaban
WERE)
sobre
el
WORKING
ON
eletromagnetismo)
discovered that the magnetic field of an electric current could BE STRENGTHENED BY
SENDING A CURRENT THROUGH A COIL (reforzarse enviando la corriente a través de
una bobina). A GREATER/HIGHER NUMBER OF TURNS IN THE COIL (mayor cantidad de
vueltas en la bobina) strengthens the magnetic field AS IT ALSO DOES/IN THE SAME
WAY AS (como también lo hace) a stronger electric current. Placing the coil AROUND
(alrededor de) a piece of iron also increases the magnetism SINCE/AS THE IRON
BECOMES MAGNETIZED/AS IRON MAGNETIZES (ya que el hierro se magnetiza.)
Not long after the DISCOVERY (descubrimiento) that A MAGNETIC FIELD COULD
BE CREATED BY (MEANS OF) AN ELECTRIC CURRENT (un campo magnético se podía
crear por una corriente electrica), M. Faraday discovered that the reverse was also true.
When a closed loop of wire is made to move through a magnetic field, .AN
EMF/ELECTROMOTIVE FORCE IS CREATED (se crea una fuerza electromotriz). THIS
MAKES A CURRENT OF ELECTRONS Ø FLOW THROUGH THE WIRE
CAUSES A CURRENT OF ELECTRONS TO FLOW THROUGH THE WIRE (Esto hace que
una corriente de electrones fluya por el cable) and is the basis for GENERATING
(generar) electricity. To generate e.m.f. the wire must cut the LINES OF FORCE (líneas de
fuerza) in the magnetic field; also THE FASTER THE WIRE IS TURNED/TURNS (cuanto
más rápido se hace girar el hilo), THE GREATER (mayor) the production of e.m.f.
Generators contain a stationary magnet, the stator, with a rotor placed BETWEEN
ITS (entre sus) north and south poles. .AS THE ROTOR TURNS (A medida que gira el
rotor), the wires in it CUT THE LINES OF FORCE (cortan las líneas de fuerza) in the
magnetic field of the stator. With each half turn the flow of current is reversed producing
alternating current (a.c.). The rotor IS DRIVEN BY A TURBINE (es movido (DRIVE) por
una turbina), a machine with huge blades moved by water or steam produced BY
BURNING COAL OR OIL (al quemar carbón o petróleo) or by nuclear fission in power
plants.
77
Transformers ARE BASED ON ELECTROMAGNETISM, TOO/ARE ALSO BASED ON
ELECTROMAGNETISM (también se basan en el elctromagnetismo). They consist OF (en)
two COILS (bobinas) of wire WOUND (enrolladas = WIND) around pieces of iron. Current
is supplied to a transformer through the primary coil and taken from the secondary.
When an ALTERNATING CURRENT FLOWS/PASSES THROUGH THE PRIMARY (corriente
alterna pasa por el primario) the constant reversal of electron flow produces a changing
magnetic field that creates a current in the secondary coil. When the primary coil has
MORE TURNS THAN THE SECONDARY (más vueltas que el secundario) voltage is
decreased; when the secondary coil has more turns than the primary, the secondary
voltage INCREASES/GOES UP/RISES (aumenta).
LISTENING: THE EFFECTS OF AN ELECTRIC CURRENT
The effects of an electric current are: THERMAL, LUMINOUS, CHEMICAL, MAGNETIC
- What happens when a current flows through a conductor? IT MAY HEAT THE
CONDUCTOR
- Which devices contain a fan to reduce this undesirable effect? ELECTRIC MOTORS
AND GENERATORS
- Is this effect always undesirable? NO. EG. DOMESTIC APPLIANCES (ELECTRIC
COOKERS) AND MANY INDUSTRIAL PROCESSES
-What else does the passage of a current through a conductor produce? LIGHT
- What happens to a conductor when the current is great enough? THE CONDUCTOR
BECOMES INCANDESCENT
- Which example does the listening give? THE FILAMENT OF A LIGHT BULB
- How is light also produced? WHEN A CURRENT IONIZES A GAS
- What colour do mercury vapour lamps give? GREENISH-BLUE LIGHT
- What is electrolysis? AN ELECTRIC CURRENT CAN SEPARATE A CHEMICAL
COMPOUND INTO ITS COMPONENTS
- How is chlorine generated? BY ELECTROLYSIS OF SALT WATER
- Which is the second example of electrolysis given in the listening? TO BREAK DOWN
WATER INTO HYDROGEN AND OXYGEN
- What substance is added to pure water and why? SULPHURIC ACID BECAUSE PURE
WATER DOES NOT CONDUCT WELL
-What other effect does a current flowing through a conductor create? A MAGNETIC
FIELD AROUND IT
This effect has three applications:
1-MAGNETIZE MAGNETIC MATERIALS AND ATTRACT THEM TO THE CONDUCTOR (e.g.
= RELAYS)
2- IF THE MAGNETIC FIELD IS CUT BY ANOTHER CONDUCTOR, AND
ElectroMotiveForce WILL BE INDUCED IN THAT CONDUCTOR (e.g.= TRANSFORMERS
AND GENERATORS)
3-IF A CURRENT-CARRYING CONDUCTOR IS PLACED IN THE MAGNETIC FIELD, A
FORCE WILL BE EXERTED ON IT (e.g.= MOTORS)
77
GUIDED WRITING
Write complete paragraphs by using the words given below. Remember that they are in the
correct order. Add words as needed.
1. MATERIALS / DIVIDE / CONDUCTORS / INSULATORS / DEPEND /PERMIT / ELECTRONS / TO FLOW /
EASILY.
Materials can be divided into conductors and insulators depending on whether/if
they permit electrons to flow easily/ how easily they permit electrons to flow
2. MOST / METALS / BE / GOOD / CONDUCTORS / BECAUSE / HAVE / LOW RESISTANCE
Most metals are good conductors because they have (a) low resistance (to
electricity)
3. HOWEVER / COPPER / BE / COMMONLY USED / METAL / WIRES / DUE / LOW RESISTANCE.
ADDITION / MALLEABILITY AND DUCTILITY / ENABLE / MAKE / COILS
However, copper is the most/a commonly used metal in wires due to its low
resistance. In addition (to this), its malleability and ductility enable us to make coils
4. CROSS SECTION / WIRE / BE / ALSO / IMPORTANT. THUS/ THICK WIRE / OFFER / LOW
RESISTANCE / FLOW / ELECTRICITY / WHEREAS / THIN WIRE / INCREASES / RESISTANCE. THICK
WIRES / BE / THEREFORE / USE / DISTRIBUTE / ELECTRICITY / POWER PLANTS / OUR HOUSES.
The cross section of a wire is also important. Thus, a thick wire offers a low
resistance to the flow of electricity, whereas a thin wire increases (the) resistance.
Thick wires are therefore used for distributing electricity from power plants to our
houses.
5. THE OTHER HAND / THIN WIRES / USE / LAMPS / BECAUSE / BE / HIGH RESISTANCE / WHAT / BE
USED / MAKE / LAMPS / SHINE
On the other hand, thin wires are used for/in lamps because it is high
resistance/high resistance is what is used for making lamps shine
EXTRA READING: ATOMS AND NUCLEI
All matter is composed of microscopic particles known as atoms which are typically about a billionth of a
centimetre in diameter (more precisely, atomic sizes range from 1 to 5 x 10-8 cm). But
these atoms also have a structure that consists of a very tiny (but massive) charged
atomic nucleus surrounded by several negatively charged electrons.
Although the atomic nucleus contains essentially all of the mass of the atom (99.9%), it is
only about one ten-thousandth as large as the atom (about 10-2 cm in diameter).
The atomic nucleus is made up of two types of particles: protons, which carry a positive
charge and neutrons, which are electrically neutral. We denote the number of protons in
the atomic nucleus by the atomic number Z. There will be an identical number Z of
negatively charged electrons orbiting about the positive nucleus, attracted to it by the electrical (or Coulomb)
forces which occur between charged objects. Since the electron charge is equal and opposite to that of the
proton, the atom itself will be electrically neutral.
Atoms can interact with one another by means of the electrical forces that arise between their electrons and
nuclei. They can bang into one another, knocking electrons loose, or acquiring or sharing electrons with one
another. Such electrical forces can cause the atoms to stick or bind together into groups of atoms or molecules.
It seems logical that since the interaction among atoms depends on their electrical charge, atoms with the same
atomic number Z will behave identically from a chemical standpoint. The chemical properties of such chemical
elements are essentially determined by the number of electrons in the outmost orbit (or shell) of the atom, since
these are the electrons that participate in atomic (or chemical) reactions. This gives rise to a classification
scheme of chemical properties of the chemical elements which is most conveniently displayed by the Periodic
Table of the Elements
Whenever atoms interact to form molecules, or molecules interact to form new types of molecules, there is
either a release or an absorption of energy. In particular, if a reaction requires that we add energy to cause it to
occur (i.e., by heating the chemical mixture), we call the process endothermic. If the reaction liberates energy, it
is exothermic. Obviously, exothermic reactions are of most interest in energy-generation schemes.
77
The energy released in such reactions arises from the electrical forces between electrons and nuclei. Atomic
energies are conventionally measured in a unit called the electron volt (eV), which is defined as the energy
required to push a single electron through a potential difference of one volt.
Although a single atomic or chemical reaction will liberate at most only several eV of energy, we must keep in
mind that an enormous number of such reactions will occur in any chemical process. For example, when we
burn 1 gram (g) of coal, we induce 5 x 10 reactions, each of which liberates 4 eV of energy, for a total energy
yield of roughly 3000 J.
We have noted that atoms can bind together to form more complicated objects known as molecules. In a similar
manner, either atoms or molecules can be attached together to form macroscopic-sized samples of matter. At
low temperatures, the atoms will bind to one another in a more or less rigid pattern which corresponds to a solid
material. Of course, even though solids appear to be quite rigid and inanimate forms of matter, on a microscopic
level the atoms are in vigorous motion, vibrating about a fixed position in the solid structure. As the solid is
heated to higher temperatures, these vibrations become more agitated until the atoms break away from their
lattice position and begin to move about in a random fashion. At this point the solid loses its structure, its rigidity.
We find on a microscopic level that the solid has melted; it has become a liquid.
Suppose we continue to heat the liquid to still higher temperatures. The atoms move more and more rapidly
until they reach speeds which are too high to allow them to be attracted to one another and clump together. The
liquid vaporizes into the gas phase. Hence, we see that the form taken by matter-the state of the matterdepends sensitively on its temperature; that is, the speed of motion of the atoms or molecules which comprise
its microscopic structure. We are used to thinking of matter as existing in one of these three states: solid, liquid,
or gas.
But there is yet another fundamental state of matter. Suppose we continue to heat the gas to still higher
temperatures. Eventually, we will supply sufficient energy to the molecules of the gas that they will knock one
another apart when they collide-they will dissociate into individual atoms. If we continue to add energy,
eventually the collisions will become so violent that the electrons will be stripped off of the atomic nuclei
(ionization), and we will find that the gas has become a collection of free electrons and positively charged nuclei
or ions. Such an ionized gas is referred to as a plasma. Plasmas are not ordinarily encountered (or at least
recognized) in our daily experiences since the temperatures required to ionize a gas are enormous, typically
ranging upwards of 10, 000 ºC. Nevertheless, plasmas are quite common in physics. For example, the glow in a
neon light is a plasma. On a more grandiose scale, the sun-indeed all stars-is a giant blob of plasma. In fact, on
an astrophysical scale, the most common form of matter is plasma.
Source: Nuclear Power J.J. Duderstadt, Marcel Dekker Inc., New York, 1979
77