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Starter: Electricity and magnetism are closely linked. In what way?

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PART I

 

UNDERSTANDING ELECTRICITY

SECTION 1

air gap amperage amplify apply (current) armature blow capacitance capacitor charge circuit circuit breaker coil conductor consume core current alternating current = AC direct current = DC cutout discharge (v,n) earphone earthing faulty feed (fed) filament frame frequency friction fuse = fuse plug gain grid hammer handle (n,v) insulator iron iron filings lead   lightning line of force make-and-break circuit moulded plastics network off-peak period overhead conductor paste plug 3-pin power plug   pole powertool pressure receiver rectifier reduce (v) relay (v) remote control repel (v) resistance rod semiconductor sensitive short circuit smoothing circuit source spring (n) transformer step-down transformer step-up transformer store (v) supply (n) switch (n) switch off switch on terminal thermionicvalve timing device tuning valve wind (wound) wire wired in parallel wired in series withstand   () : : , , , , , , , () () , () , , , () ; , () , , , () , , , , , , , () , , () , , , , ' ' , onip  

 

SECTION 2

 

UNDERSTANDING ELECTRICITY

 

 

The word electric comes from the Greek word for amber, electron. Amber is a fossil resin, yellowish in colour. It is found on the southern shores of the Baltic Sea.

Thousands of years ago, man discovered that when amber is rubbed with fur or cloth it will attract small light objects, for example, particles of dust. It does this in the same way that a magnet will attract pieces of iron. This discovery was, perhaps, the first step made towards mans understanding of electricity.

Today we know that this attraction of small particles or objects is caused by an electrical charge, which is given to the amber by the friction, or rubbing together, of the materials. This is known as static electricity.

An electric current is the flow of electrons. To understand what an electron is, we must first think of matter and how it is constructed, or made up.

The smallest piece of any substance is called an atom. An atom is made up of a proton, which has a positive electrical charge, and a number of electrons, which have a negative charge. When the two charges are equal, the atom is said to be neutral.

Until an atom is charged, it will remain in its original form. It is held together because opposite charges are attracted to each other. Similar charges of electricity will repel. These are the two fundamental laws of electricity.

Electricity is made in many ways.

One way is by battery, as used in a transistor radio. A simple battery has a positive terminal, or pole, connected to a carbon rod. The terminal may be coloured or marked with a cross. The carbon rod is placed in a chemical paste inside a zinc container. Attached to the zinc container is the negative terminal, coloured dark or marked with a short horizontal line. The action of the chemical causes the poles to be charged.

A simple battery converts chemical energy into electrical energy. Condensers, or batteries can store small amounts of electrical power. But its not possible to store the great quantities that we use every day in our homes and in industry. The generating stations must be operating continuously to cope with this demand. There are certain times during the day, when this demand for power is very high and other times when it may be very low. These are known as peak and off-peak periods. In order to operate the power stations more efficiently they are all connected to a grid system, which is a network of high voltage cables to ensure a more even distribution of power all over the country.

A great natural source of electricity is lightning. The dazzling flash of light we see during a thunderstorm is caused by the discharge of electricity from one cloud to another. Sometimes the discharge may be from a cloud to earth. In this case the electricity may pass through a tree or a house. When this happens we say that the house is struck by lightning. To avoid the risk of damage to buildings a lightning conductor is used. It is made from a metal rod placed high on the building, which is connected by a thick conductor wire to a metal plate buried in the earth. If lightning strikes the building, the charge is conducted safely to earth.

Electricity and magnetism are closely connected. Each may be used to produce the other.

Around the poles of a magnet is an area called a magnetic field. In this area the magnet exerts its attraction. The directions of this attraction and the shape of the magnetic field are shown by lines of force. These lines of force can be seen if a small magnet is placed under a sheet of paper onto that iron filings are sprinkled.

II

 

When an electric current flows through a conductor, a magnetic field is set up around it. The conductor becomes a magnet. If a conductor is made to rotate in a magnetic field, a pressure of electricity, called a voltage, is produced in it. This is the principle on which a dynamo produces electricity.

Electricity flowing through a conductor may be likened to water flowing through a pipe. The amount of electricity that flows is measured in units called amperes. The voltage is measured in volts. Just as a thin pipe will not allow as much water to flow through it as a large one, so thin conductor will not allow as much electricity to flow as a thick one. The restriction to the flow caused by the conductor is known as its resistance. A unit of resistance is called an ohm. The resistance of a conductor will also vary according to the material of which it is made. Copper has a much lower resistance than other common metals. It is a very good conductor.

Current, voltage and resistance bear a definite relationship to one another. Ohms law tells us that current equals voltage divided by resistance. The current and the voltage multiplied together determine the power, the rate at which the electrical energy is used up by being converted to other forms of energy. A unit of power is watt.

To simplify the figures used for great power, abbreviations are used. One thousand watts is a kilowatt and one million watts is a megawatt. Very sensitive instruments can measure a milliwatt, which is a thousandth part of a watt. A millionth part of a watt is a microwatt. Electrical appliances are described according to the amount of power they consume; we talk of a 60 watt lamp, a 2 kilowatt fire.

In some pieces of electrical apparatus it is sometimes necessary to store an electrical charge, to build it up and hold it for some time. This is done by means of a capacitor, sometimes called a condenser. A simple capacitor is made from two metal plates, called electrodes, which are separated by an insulating material such as air, paper, or mica, called the dielectric.

III

 

The unit of capacitance is called a farad. This is a relatively large unit. Many capacitors used in electronic apparatus are rated in microfarads, millionth part of a farad. It is sometimes necessary to use a capacitor whose value can be varied. An example of this is the tuning control on a radio receiver, when it is turned the value of the capacitor is changed.

The most common way of making electricity is by the conversion of mechanical energy. A dynamo is a machine that makes electricity when it is made to rotate at high speed. A turbine that is rotated by steam pressure often drives it. This machinery is then called a turbo-generator. A building which houses a turbo-generator is called a power or generating station. A station that uses the power of falling water is known as a hydroelectric station. Most of the worlds electricity for domestic and industrial use is made r generated in such power stations.

Any material that will allow electricity to flow through it is called a conductor. Most metals are good conductors. Any material that will not permit the flow of electricity is known as an insulator.

Conductor wires, or leads, in any piece of electrical apparatus or installation must not be allowed to touch each other, or any other metal part. If they do, a short circuit will result which will cause failure of the apparatus and the possible dangers of fire and electric shock.

Insulating materials are used to cover and protect conductor wires and sometimes to separate them. Common insulating materials include air, oil, glass, porcelain, mica, rubber and plastics. Heavy power cables are sometimes given an extra cover, known as a bonding or shield, made of metal for the further protection of the insulation.

Two different kinds of electricity are used to operate electronic apparatus.

One kind is called direct current, usually abbreviated to DC.

This is the kind of electricity we get from a battery, the flow of current is in one direction only. The other kind is alternating current, usually known as AC. This is the kind of electricity that is generated in power stations for domestic and industrial use. It is called alternating current because the direction of flow changes very quickly. The number of changes of direction, called cycles, in every second is known as the frequency.

IV

 

The frequency of the alternating current in most parts of Europe is 50 cycles. In North America its 60 cycles. Very high frequencies are used in radio communication, sometimes several million cycles.

Electricity can be very dangerous if it is carelessly used. A faulty installation or a defective piece of equipment can cause a serious fire and there is also the danger of an electric shock, with possibly fatal consequences. Many precautions are taken and safety devices are used to minimize these dangers. Insulation, earthing, fuses and automatic cutouts are among the most common safety devices.

Insulating is the converting of a conductor with a non-conducting material to prevent it from touching another conductor. The material used vary according to the nature of the conductor and the condition in which it is used. It may have to withstand extremes of temperature and resist corrosion. The insulation of power leads to portable appliances must be flexible and also very strong.

Any piece of electrical apparatus which has a metal body or frame, especially portable appliances such as electric irons, kettles and power tools, must be earthed as a safety measure. Connecting the metal body or frame directly to earth with thick conductor brings about earthing. In a three-pin power plug the thickest pin is always the earth connection.

If a fault should develop inside the apparatus or if the insulation on a flexible lead should break down, any possibility of a person getting an electric shock by touching the apparatus will be avoided because the current will take the easier path back to earth.

As an additional precaution the handles of all such appliances are made of an insulating material such as rubber or molded plastics.

The most common safety device and one that is used in every household installation is the ordinary fuse. This is simply a piece of wire that is connected in series in the circuit. It is of such a resistance that it will melt and therefore break the circuit if the current flowing in the circuit exceeds a certain amount. When this happens we say the fuse blows. It is very important that fuse wire of the correct amperage is used.

It is often necessary to increase or decrease the voltage of the electricity supply. One reason for this is the economic transmission of power from its source, the generating station, to wherever it is required for use, which may be at a great distance. It is cheaper and easier to carry a very high voltage but low current, over long distances. It can be done using thinner overhead conductor wires, with an air gap between them to act as an insulator.

When the overhead cables reach the area where the electricity is required for use, the voltage must then be carried by much heavier conductors, which have to be well insulated and are therefore more costly.

V

 

A transformer is used to increase or decrease the voltage of an electric power supply. A transformer is a static machine it has no moving parts. It consists of two coils of wire that are wound around a soft iron core. The coils are called windings, one is the primary, or input winding, and the other is the secondary, or output winding.

When a current is passed through the primary winding, a magnetic field is set up around the iron core that induces a voltage in the secondary winding. If the number of turns in the secondary is greater than the number in the primary it is a step-up transformer and the output voltage is greater than the input. A step-down transformer reduces the input voltage.

Some complicated pieces of electrical apparatus, for example radio and television receivers, do not use alternating but direct current. As the domestic supply is alternating current, it is therefore necessary to change it to direct current inside the apparatus. This change, or conversion, is brought about by means of a rectifier, sometimes called a diode.

A simple diode consists of a valve that has only two electrodes; one is the anode and the other the cathode. When it is used to rectify, it will pass current only during each half cycle of the applied alternating current. The result is a pulsating current flowing in one direction, an irregular, or uneven current, but a direct current. It can be made regular and even by means of a smoothing circuit.

A valve is a device that allows a flow in one direction only. In a radio valve this is the flow of electrons from cathode to anode. A simple thermionic valve is called a diode because it has two electrodes: the cathode, which is negative, and the anode, which is positive. It is called a thermionic valve because the cathode is in the from of a filament and when it becomes hot, negative electrones become free and are attracted towards the positive anode.

There are many different kinds of valves in a radio receiver; they are specially designed to perform different functions. A triode is a valve with three electrodes, an anode, a cathode and a control grid. A tetrode has four, and a pentode five electrodes.

A major development in the electronics industry during recent years has been the gradual replacement of thermionic valves by transistors. A transistorized circuit is simpler, smaller, and technically stronger. Because of these advantages the transistor has contributed greatly to rapid developments in other scientific fields, particularly space travel.

VI

 

A transistor is a semiconductor. This means that it is not entirely a conductor, nor is it an insulator. It is crystalline in structure and has three electrodes, a base, an emitter and a collector.

The main difference between a valve and a transistor is that while a valve amplifies, or gives a voltage gain, a transistor gives an increase in current. Transistors can be made from germanium, selenium, silicon and other substances.

The various components that go to make up a complicated electrical circuit may be connected to the circuit in two ways. If the supply is fed directly through each component in turn, they are said to be wired in series. If, however, the supply is taken to each one independently then they are wired in parallel.

Every component in series in a circuit will add to the total resistance of the circuit and decrease the current flowing through it, but every additional resistance in parallel will reduce the total resistance of a circuit. A high-tension battery is made up of a number of small batteries connected in series. Its voltage is equal to the sum of the voltages of the smaller batteries.

A switch is used in almost every piece of electrical apparatus. Its purpose is to make complete or to break an electrical circuit. When a circuit is switched on it is a closed circuit and current will flow through it. When it is switched off the circuit is broken, it becomes an open circuit and the flow of current is stopped. The main contacts of a switch are called poles. These are connected when the switch is on.

There are very many different kinds of switches ranging from a micro-switch, which is very sensitive, to the large and complicated ones, which are used for high voltages and are sometimes known as circuit breakers. Temperature or pressure control or timing devices can operate switches automatically.

It is sometimes convenient or economical to operate electronic apparatus from a distance. This is known as remote control and it may be brought about by the use of a relay, which is really an electromagnetic switch.

A relay consists of an electro-magnet which, when energized attracts a soft iron armature. The armature is returned to its former position by a spring when the electro-magnet is de-energized and therefore there is no longer any attraction. The movement of the armature opens or closes the contracts of the relay. In this way one electrical circuit can be used to control another.

The telephone uses very little electric current. It consists of two main parts, the microphone and the earphone.

The microphone contains a very thin and flexible metal disc called a diaphragm. It also contains a magnet. When we speak we cause the diaphragm to vibrate. The movements of the diaphragm in the magnetic field set up a varying electrical current. The current is carried along wires to the earphone of the person to whom we are speaking.

The earphone contains a small electro-magnet and a diaphragm similar to the one in the microphone. The varying current is fed into the electro-magnet and causes it to exert a varying attraction on the diaphragm, which vibrates and so reproduces the sound that went into the microphone.

An electric bell is made to work by a make-and-break circuit It consists of an electro-magnet whose armature is the hammer of the bell. The circuit includes a pair of contracts, one of which is attracted to the armature. A spring holds the armature in such a position that the contacts are closed.

When the operating button is pushed, the electro-magnet attracts the armature against the tension of the spring, and the hammer strikes the bell. At the same time, the contacts are opened, and so the circuit is broken and the spring returns the armature to its former position. The contacts are now closed again and as long as the button is pushed the armature will vibrate and the bell will continue to ring.

SECTION 3

EXERCISE 1. Spell and translate the words transcribed below:


EXERCISE 2. Choose Ukrainian analogues to match the terms:

 

collector amperage positive neutral diaphragm   electric label dynamo battery pole generate kilowatt contract transformer cycle communication electronic apparatus generating station relay voltage

 

EXERCISE 3. Guess the meaning of the derivatives below by singling
out their roots:

plastic, transformer; pressure; rotate; amperage; static; de-energized; thermionic; voltage; terminal; oppose; condenser; primary; passed; portable; lightning

 

EXERCISE 4. Pick out the terms corresponding to the Ukrainian ones below:

(2) (2) / ()   () () () () , / ,   , (3) /     / ( )     , (2)    

EXERCISE 5. Shorten the sentences to the rate of useful information:

1. Thousands of years ago, man discovered that when amber is rubbed with fur or cloth it will attract small light objects.

2. Any material that will allow electricity to flow through it is called a conductor.

3. A dynamo is a machine that makes electricity when it is made to rotate, or turn, at high speed.

4. Around the poles of a magnet is an area called magnetic field in which the magnet exerts its attraction.

5. The amount of electricity that flows called current, is measured in units called amps.

6. The current and the voltage multiplied together determine the power, the rate at which the electrical energy is used up by being converted to other forms of energy.

7. Conductor wires, or leads, in any piece of electrical apparatus or installation must not be allowed to touch each other, or any other metal part.

8. There are very many different kinds of switches ranging from a micro-switch, which is very sensitive, to the large and complicated ones that are used for high voltages and are sometimes known as circuit breakers.

9. Some complicated pieces of electrical apparatus, for example radio and television receivers do not use alternating but direct current.

10. When the overhead cables reach the area where the electricity is required for use, the voltage must then be carried by much heavier conductors, which have to be well insulated and are therefore more costly.

11. A simple thermionic valve is called a diode because it has two electrodes: the cathode, which is negative, and the anode, which is positive.

 

EXERCISE 6. Divide the text into portions according to the sense and entitle them

EXERCISE 7. Parts of the text are mixed up. Arrange the portions consequently according to the contents.

EXERCISE 8. Write the summary of the text and prepare an oral report: The Nature of Electricity.

 

EXERCISE 9. A. Translate the text Solar Energy.

 

SOLAR ENERGY

Shortage of energy is a major world problem and experts predict that the present rate of increase in energy use could exhaust the supply of fossil fuels in the twenty-first century. What the world needs is a source of perpetual energy.

Potentially, we have a source of perpetual energy shining down on us. The sun. On clear day in the tropics, the intensity of solar energy can be more than a kilowatt per square metre at mid-day. That amount of energy falling on an area of sixty-four square kilometres is about as much as the whole of the British electricity generating system produces.

There is no charge for the energy that flows so freely from the sun..

Unfortunately its collection and storage can be both difficult and expensive. Some form of storage is necessary because the suns rays do not reach us on cloudy days or at night. Never the less, solar energy is now an economic and practicable solution and is widely used in many countries.

It is possible to convert solar energy directly to electricity by the use of

photoelectric cells but for most practicable purposes this is too expensive a way to

produce electricity. Todays solar energy systems are of two main types, based on the

flat plate collector and the focusing collector. The flat plate collector is simpler and

cheaper. In its simplest form, the suns rays fall onto a panel. Pipes carrying water are

embedded in the panel. The sun heats the water, which is then available for use.

Modern flat plate collectors are carefully designed to absorb the maximum possible amount of energy and to prevent heat loss to the surroundings. They are mainly used for the provision of domestic hot water. They are commercially available and are in use in many countries including Australia, Japan, Cyprus, Brazil and Israel.

 

B. Look up the dictionary for the following words:

 

Exhaust   Perpetual   Expensive   Ray   Pipe  
Fuel   Amount   Reach   Available   Embedded  
Source   Charge   Cell   Flat   Surroundings  

 

C. Find the terminology youve come across in the main text.

 

EXERCISE 10. Make a précis of the main text using the technique of exercise 5.

EXERCISE 11.Write an annotation of the text Solar energy.

PART II

ELECTRICITY AND MAGNETISM.

LESSON 1

Step 1.

Pre-text exercises.

Make sure that you know these words:

 

material; phenomenon, (pl) phenomena; manifestation; magnetism;

induction; practical; period; telegraph; telephone; Coulomb; machine;

associate; chemical; concentrate; oxide; sulfate; proportion; arc; energy, nature.

Step 2.

Give English equivalents to the Ukrainian words and word -combinations in brackets and translate the sentences into Ukrainian.

1. When we rub (i) substances, notably () and () with () or (), they () the (1) to attract small ( ) and ().

2. This () is the manifestation of electricity.

3. ( ), the ability of certain ( ) such as ( ) to attract small bits of iron is a manifestation of magnetism.

4. All these things were known from ( ).

5. Most of the basic ( ) of electricity and magnetism were discovered between 1784 and 1831.

6. Michael Faraday discovered magnetic ().

7. ( ) the only practical electrical (). Was the ().

8.The practical utilization of electricity () rapidly with development of the telegraph, the telephone, incandescent lighting and electric motors

9. Uses of electricity () to this day with the ( ) in microelectronics.

10. Microelectronics gives us ( ) over the machines

 

THE NATURE OF ELECTRICITY.

Input

The only way to charge a body negatively is to add electrons to it, and the only way to charge it positively is to take electrons away from leaving an excess of positive electricity.

The ancient Greeks knew that when a piece of amber is rubbed with wool or fur it achieves the power of attracting light objects. Later n phenomenon was studied, and, the word electric, after the Greek word electron, meaning amber was used. Many scientists investigated electric phenomena, and during the nineteenth century many discoveries about the nature of electricity, and of magnetism, which is closely related to electricity, were made. It was found that if a sealing-wax rod is rubbed with woolen cloth, and a rod of glass is rubbed with a silken cloth, an electric spark will pass between the sealing-wax rod and the glass rod when they brought near one another. Moreover, it was found that a force of attraction operates between them. An electrified sealing wax is repel let however, by a wax rod, and also an electrified glass rod is repelled, by similar glass rod.

The ideas were developed that there are two kinds of electricity, which were called resinous electricity, and that apposite kinds of electricity attract one another, whereas similar kinds repel one another. Although these simple electric and magnetic phenomena have been known since ancient times, most of the basic quantitative laws of electricity and magnetism were discovered between 1784, when Charles Coulomb investigated the forces between charged objects, and 1831, when M. Faraday discovered magnetic induction. Prior to this 50-year period of discovery, the only practical electric invention was the lightning rod of Benjamin Franklin (1752).

After this period, the practical utilization electricity increased rapidly with the development of the telegraph (1844), the telephone (1877), incandescent lighting (1880) and electric motors (1887). Uses of electricity have continued to expand to this day, with the current revolution in microelectronics giving us ever-increasing control over the machines.

The study of electricity may be divided into three classes or branches: magnetism, electrostatics, and electrodynamics. Magnetism is the property of the molecules of iron and certain other substances through which they store energy in a field of force because of the arranged movement of the electrons in their atoms. Electrostatics is the study of electricity at rest, or static electricity. Examples of this type of electricity are charges on condenser plates. Rubbing glass with silk produces static electricity. Electrodynamics is the study of electricity in motion, or dynamic electricity. The electricity that flows through wires for light and power purposes is a good example of latter type of electricity.

 

Step 3

Say what physical phenomenon the text is concerned with.

 

Step 4

Find the part of the text dealing with the fundamental forces of nature.

Discuss the information with your fellow students.

 

Step 5

Answer the following questions embracing the contents of the text.

1. What is the way to charge a body negatively or positively?

2. What capacity did amber and glass acquire when rubbed with silk or fur? .

3. What is magnetism?

4. When were the basic quantitative laws of electricity and magnetism discovered?

5. When did C, Coulomb investigate the forces between charged objects?

6. When did M. Faraday discover magnetic induction?

7. What was invented by B. Franklin?

 

Step 6.

Make up a short dialogue on the following situation;

1. A few students make an experiment with different materials to receive electricity.

2. Ask your fellow-student- about history of electricity and magnetism.

 

LESSON 2

Oersted and Faraday.

 

Step 1.

Draw a diagram to illustrate the second part of the experiment. Label the diagram with these words; wire bridge; battery; terminals; pivoted needle direction of deflection; connecting leads.

Step 2.

Are the following statements true or false? Correct any that is wrong.

a) Oersted was trying to show that electricity and magnetism were not related.

b) For this experiment he used a kind of compass needle, a wire bridge and an electric generator.

c) He first placed the magnetic needle underneath the wire, then connected the wire to the battery.

d) The needle under the wire was pushed first one way, then the other.

e) In the second part of the experiment he put the needle above the wire.

f) The needle above the wire was not deflected at all.

g) Oersted thought the wire was surrounded by a magnetic field.

Step 3.

Find words and expressions in the Input with similar meanings to the followings: free to turn, pushed away, beneath, connection, carrying an electric current, apparatus, a form of, put.

 

Step 4.

The bottom diagram represents the magnet in the top diagram broken into pieces. None of the pieces has been moved. Draw the bottom diagram and mark in the poles.

N S

 

Step 5.

Why is Oersteds experiment described as the first step towards the invention of the generator or dynamo?

 

Steps 6.

Here are the instructions for a simple experiment with a magnet. You have just done this experiment.

Now write the report. Start like this: The aim of the experiment was to show why the like poles of a magnet repel and the unlike poles attract. We took...Continue.

 

Why do the like poles repel?

Take a sheet of cardboard, a magnet, a handful of iron filings and a compass. Put the magnet under the sheet of cardboard and scatter the iron filings on the top of the card.

Tap the edge of the card lightly. The iron filings will make a pattern. They will form a series of loops between the two poles of the magnet. Place the compass on one side of the magnet and then on the other. You will see that the compass needle follows the loops. This shows that there are lines of force, which leave the magnet at one pole and enter it again at the other pole.

 

Step 7.

Reporting writing

a) Look at your answers to Step 2. The true statements and your corrected statements make a summary of the Oersteds experiment.

Step 8.

Read this description of one of Faradays experiments and make a summary of it. Use the structure you practiced in Step 7

 

Oersteds experiments did not have any immediate practical application. All he had done, in effect, was to show that a wire carrying an electrical current acts like a magnet. The thing that most interested scientists was the question of whether the opposite was true, could magnets be used to induce an

electric current?

Michael Faraday an English scientist carried out a series of experiments to find the answer to this question. His work led to the development of the electric generator and so made it possible to produce electricity on a large scale.

In one of his experiments, Faraday connected a coil to a simple ammeter. Then he took a bar magnet and moved it quickly towards the coil. The ammeter showed a momentary current. When the magnet was moved quickly away from the coil, the ammeter again registered a current but in the opposite direction.

Faradays experiments were only the first steps, but he had shown quite clearly that magnets could be used to produce an electric current. The next step was to show that a momentary movement should induce a continuous current. This is the principle on which all electric generators (and motors) are based

 

LESSON 3

STUDY SECTION

 

Copper is a good conductor of electricity. If a copper wire is connected to a battery, an electric flows in the wire. However a current does not flow if you connect a piece of plastic to the battery. Because plastic is an insulating material, it resists the flow of electricity. Bad conductors of electricity have a high resistance.

 

Look at this diagram. It shows an electric circuit:

battery

wire

lamp gap.

 

Place a piece of copper wire across the gap. The lamp lights. Current flows around

the circuit. After removing the copper, place a piece of nichrome across the gap. The

lamp is dimmer. Nichrome has a high resistance and the current does not flow easily.

This fire uses electricity for heating. The heating element is made of nichrome, which

is a bad conductor of electricity. It has a high resistance and current cannot flow

easily. Therefore, the current passing through the element generates heat.

 

Step 1.

Are these statements true or false? Correct the false ones.

1. An insulator is made of a material, which resists the flow of electricity.

2. An electric current flows easily through a good conductor.

3. If a copper wire is connected to a battery an electric current flows.

4. Nichrome is a good conductor of electricity.

5. If you pass an electric current through nichrome, heat is generated.

6. Rubber has a low resistance to electric current.

7. An electric current flows easily through a material that has a high resistance.

8. The lamp is dimmer when a smaller current flows.

 

Step 2

 

V Voltmetter.

S Switch A Ammeter

Make statements about symbols.

For example:

This is the symbol used for a lamp in an electric circuit diagram A V

(An ammeter is used for measuring electric current. A voltmeter is used for measuring electric energy). Now look at the circuit diagram and read this: The battery is in the middle of the diagram at the top and a voltmeter is connected across it. The lamp is on the left, towards the top, the ammeter is on the right, towards the bottom. The switch is positioned at the bottom and on the left. Now read this and draw the circuit diagram, which is described. The battery is in the middle of the diagram at the bottom and a voltmeter is connected across it. On the right of the diagram is a lamp, which is positioned towards the top. The ammeter is on the left and in the middle and the switch is at the top on the right.

 

Step 3.

Look at this circuit diagram and complete the description V A

The battery ........ in the ........ of the ........ at the ........ and a ... it.

The ....... is in ....... .on ...... right. The lamp is on ........ towards . . . . switch .........

 

Language Point

Resistance is measured in ohms (W)

Current (I) is measured in amps (A)

Voltage (V) is measured in volts (V)

This formula is used to calculate the resistance in a circuit.

V=IR (V equals I times R.)

 

Fill in the gaps:

V- voltage measured in volts,

I-

R-

Look at this circuit diagram: R is the symbol for a resistor. A resistor is made of a material, which resists the flow of electricity. Some resistors are made of nichrome.

To calculate the voltage, V:

V=IR=53t!2=l

V=10 volts

Read out the calculations in full, for example, voltage equals current times resistance, which is five times two.

Now calculate the current, voltage and resistance in the following circuits:

Calculate I Calculate V Calculate R

 

Step 4

Put in the right words. The first one has been done for you.

1. If you connect a copper wire to a battery a current flows.

2. After ... the copper, place a piece of nichrome across the

3. An insulator ... the flow of electricity.

4. An ... is used for ... current.

5. ... is measured in ohms.

6. A voltmeter is connected ... a battery.

7. The switch is ... the top ... the right.

8. Draw a ... diagram that has a battery on the right.

9. Heat is ... when you pass an electric current ... nichrome.

10. To calculate the voltage use this ... .

 

Step 5.

1. If the torch uses 0.5A, the calculator 0.05A, the cassette player 2A, calculate the resistances.

2. On the back of most electrical devices there is the power rating

SONNY JAPAN

MODEL 36

SERIAL 0169423/005

6W 6V

Use this formula for calculating the power of an electrical device

R=IV

Power, P, is measured in watts (W). The power rating of the device is 6W.

Calculate the current that is used

P=IV 6=16 6/6=1 I=1A

 

Look at this table. Fill in the gaps:

electrical device:

power (W)

voltage (V)

current (I)

Electric fire light bulb electric drill

2400 W 55 W 990W

240 V 110V 110V

electric kettle; car headlight; television;

---- 48W 20W

240V 12V 110V

10A ---- ---

Now make statements like this example.

The electric drill has a power rating of 990W. When it is connected to a main supply of 110 volts it uses a current of 9A.

 

 

Step 6.

Fuses usually have four different ratings: , 5A, 10A, I3A.

Make statements about the electrical devices in Step 5 like this example. Use a I3A fuse with an electrical kettle because it draws a current of 10A.

 

Step 7

1. Calculate the resistance of the electrical devices in Step 5.

2. Find out the power rating of other electrical devices, for example, an electric cooker, washing machine, radio, etc.

Language Point

240V - two hundred and forty volts 50A - fifty amps.

LESSON 4

 

Fuses

Starter: Any electrical circuit usually has one or more fuses in it. Why? What would happen if there were no fuses?

Input: Safety with Fuses.

If an appliance such as a light or a heater stops working, it is probably because the fuse has blown. There are 3 main types of fuse in use today - cartridge, rewirable and the most modern type, miniature circuit breakers. Some appliances have their own fuses (usually in the plug), so this should be checked first. Otherwise, check whether the main fuse has gone. The main fuses are normally in a switch box or fuse box at the point where the main electricity supply cable enters the building usually near the front door. Before checking these fuses, turn off the main switch. Remove and examine the fuses one by one. Which the cartridge fuses the simplest thing to do is to take out the old fuse and try a substitute fuse of the correct amp rating, of course.

Then test the appliance, with reliable fuses look for wire breaks or scorch marks on

the fuse carriers. Remove the old wire, fit new wire round the retaining screws and

tighten the screws. Replace the fuse carrier and see if the appliance works. If a fuse

continues to blow, do not fit another fuse, but get an electrician to check the

appliance and the circuit for possible faults. Never attempt to use a fuse of a higher

rating.

Gathering Information

 

Step 1.

From Input, find answers to these questions :

What does a fuse do?

What are the three types of circuit protection?

Where are fuses located in a circuit?

How should you check a cartridge fuse?

What tells you whether a reliable fuse has blown?

What is the first thing to do when checking a main fuse?

What should you do if a new fuse blows immediately?

 

Step 2.

Replace the words and expressions in bold type with ones of similar meaning from the Input.

a) When a rewirable fuse blows, it burns the carrier.

b) Always switch off, before examining the main fuses.

c) When you have put the fuse back, try the appliance again.

d) There is probably something wrong with the circuit, if the fuse blows again.

e) With a reliable fuse you must take out the old wire, then put new wire round the screws and do up the sewers.

 

Step 3

a) What are the advantages and disadvantages of the different types of fuses mentioned?

b) Why shouldnt you fit a fuse of a higher rating?

 

Step 4.

Warnings

Do:

Always turn off the main switch

Always fit a fuse of the correct rating.

 

Dont:

Dont fit a fuse of

Do not do a higher rating.

 

Make warnings from these cues:

a. Check the amp rating of an appliance

b. Handle electricity with wet hands

c. Repair appliances with the power on

d. Use insulated pliers

e. Put too many plugs to one outlet

f. Use old cables or flexes

g. Have a supply of fuse wire available

h. Join wires carelessly.

Step 5.

Conditions and Instructions

 

Look at these examples:

If an appliance stops working, check the fuse.

If a fuse continues to blow, do not fit another fuse.

Choose a condition from A and an instruction from B to make sentences like those in the examples :

A An appliance stops working. You do not know where the fuse box is. You havent got the correct amp fuse. You need to check the main fuse. You know little about electricity. One of the circuit breakers is switched off. Check whether one of the switches is off. Look near the front door. Check the appliance fuse first. Use a higher amp rating. Check the circuit or appliance. Try to fit electrical faults yourself. Switch the circuit on again. B The appliance has got its own fuse. The fuses are reliable. The fuse blows again immediately. The fuse continues to blow. You have got circuit breakers. The appliance has not got a fuse.   Check the main fuses. Leave the fuse box switched on. Fit another fuse. Check the fuse. Fit a new fuse. Look for scorch marks.  

 

LESSON 5

THE ELECTRIC MOTOR

Step 1.

List as many items as you can in the home, which use electric motors.

Reading skimming

A very useful strategy is reading a text quickly to get a general idea of the kind of information it contains. You can then decide which parts of the text are worth reading in more detail later, depending on your reading purpose. This strategy is called skimming.

 

Step 2.

Skim this text and identify the paragraphs, which contain information on each of these topics. The first one has been done for you.

a) What electric motors are used for paragraph 1?

b) Why the armature turns?

c) The commutator.

d) Electromagnets

e) Effect of putting magnets together.

f) The armature paragraph in an electric motor an electric current and magnetic field produce a turning movement. This can drive all sorts of machines from wrist-watches to trains. The motor that is used for example for a washing machine. It is an universal motor that can run on direct current or alternating current.

 

An electric current, running through a wire produces a magnetic field around the wire. If an electric current flows around a loop of wire with a bar of iron through it, the iron becomes magnetized. It is called electromagnets: one end becomes a North Pole and the other a South Pole, depending on which way the current is flowing around the loop.

If you put two magnets close together, like poles-torn example, two north poles - repel each other, and unlike poles attract each other. In a simple electric motor, a piece of iron with loops of wire round it, called an armature, is placed between the north and South poles of a stationary magnet known as the field magnet. When electricity flows around the armature wire, the iron becomes an electromagnet.

The attraction and repulsion between the poles of this armature magnet and the poles of the field magnet make the armature turn. As a result, its north pole is close to the south pole of the field magnet. Then the current is reversed so the north pole of the armature magnet becomes the South Pole. Once again, the attraction and repulsion between it and the field magnet make it turn. The armature continues turning as long as the direction of the current, and therefore its magnetic poles, keeps being reversed.

To reverse the direction of the current, the ends of the armature wire are connected to different halves of a split ring called a commutator.

Current flows to and from the commutator through small carbon blokes called brushes. As the armature turns, first one half of the commutator comes into contact with the brush delivering the current and then the other, so the direction of the current keeps being reversed.

Source: Adapted from I snide out: Electric Motor, Education Guardian.

 

Step 3.

Match each of these motor components to its function, and then describe its function in a sentence

Component Function

1 armature a) transfers rotation from the motor;

2 bearing b) create an electromagnetic field;

3 brushes ) converts electromagnetic energy to rotation;

4 commutator d) reverses the current to the armature

5 drive shaft e) support the drive shaft;

6 field windings f) supply current to the armature;

Step 4. Complete the text. Use the following words: are made up; is placed; is composed; consists.

 

A transformer ... of two coils, a primary and a secondary. The coils are wound on a former which is mounted on a core. The coils ...of a number of loops of wire. The core ... of thin pieces of soft iron.

U- and T- shaped pieces are used.

 

Word study

Study these expressions for describing how components are connected to each other.

 

A is bolted to B. = A is connected to with bolts.

A is welded to B. = A is connected to B by welding.

A is fixed to B. = no specific method given.

 

Step 5.

Explain each of these methods of connection

1 screwed 2 soldered 3 attached 4 wired 5 bonded   6 nailed 7 brazed 8 welded 9 riveted 10 glued  

 

 

LESSON 6.

Step 1.

Step 2.

Answer these questions about a portable generator using your own knowledge of engineering.

1 What are its main parts?

2 What does the engine run on?

3 What are the four strokes called?

4 What is the function of the crankshaft?

5 What do both stator and rotor have?

6 What is the difference between stator and rotor?

 

Step 3.

Read this text to check as many of the answers as you can. You will not find complete answers to all of the questions.

 

PORTABLE GENERATOR.

 

Although most electricity comes from power stations power can also be generated by far smaller means. Nowadays, electricity generators can be small enough to hold in the hand.

Portable generators are made up of two main parts: an engine, which powers the equipment, and an alternator, which converts motion into electricity.

The engine shown (Fig.1) runs on petrol. It is started by pulling a cord. This creates a spark inside which ignites the fuel mixture. In a typical four-stroke engine, when the piston descends, the air inlet valve opens and a mixture of air and petrol is sucked in through a carburetor. The valve closes, the piston rises on the compression stroke and a spark within the upper chamber ignites the mixture. This mini-explosion pushes the piston back down, and as it rises again the fumes formed by the ignition are forced out through the exhaust valve.

This cycle is repeated many times per second. The moving piston makes the crankshaft rotate at great speed.

The crankshaft extends directly to an alternator, which consists of two main sets of windings - coils of insulated copper wire wound closely around an iron core. One set, called stator windings, is in a fixed position and shaped like a broad ring. The other set, the armature windings, is wound on the rotor, which is fixed to the rotating crankshaft. The rotor makes about 3,000 revolutions per minute.

The rotor is magnetized and as it spins round, electricity is generated in the stator windings through the process of electromagnetic induction. The electric current is fed to the output terminals or sockets. This type of generator can produce a 700watt output, enough to operate lights, television, and some domestic appliances. Larger versions provide emergency power to hospitals and factories. Source adapted from Inside out: Portable generator. Education Guardian.

Step 4.

Study this text on the four-stroke cycle. Then label each stroke correctly.

 

In the four-stroke cycle, the piston descends on the intake stroke, during which the inlet valve is open. The piston ascends on the compression stroke with both valves closed and ignition takes place at the top of the stroke. The power or expansion stroke follows. The gas generated by the burning fuel expands rapidly, driving the piston down, both valves remaining closed. The cycle is completed by the exhaust stroke, as the piston ascends once more, forcing the products of combustion out through the exhaust valve. The cycle then repeats itself.

 

Language study: Cause and effect.

Step6.

Rewrite these sentences replacing the phrases in italics with appropriate -ise/-ize verbs.

1. Some cars are fitted with a security device, which makes the engine immobile.

2. In areas where the power supply fluctuates, for sensitive equipment a device to make the voltage stable is required.

3. Manufacturers seek to keep costs to a minimum and profits to a maximum.

4. Most companies have installed computers to control their production line.

5. Companies may make their operation more rational by reducing the variety of products they make.

 

Step 7.

The statements that follow describe the distribution of power from power station to consumer. Put the statements in the correct order. The first one has been done for you.

a) It is fed to substations.

b) It is stepped up by a transformer to high voltages for long-distance distribution.

c) It is distributed via the grid to supply points.

d) It is distributed to the domestic consumer.

e) Electricity is generated at the power station at 25 kV.

f) It passes via the switching compound to the grid.

g) It is distributed via overhead or underground cables to intermediate substations.

 

Step 8.

Mark the sequence of stages using appropriate sequence words where you think this is helpful. Add the following information to your statement and make them into a text.

1. At the main grid supply points, power is stepped down to 33kV for distribution to heavy industry.

2. At intermediate substations, power is reduced to 11 Kv for light industry.

3. At the distribution substations, power is stepped down to 415 V. 3-phase, and 240 V, 1-phase.

 

Technical reading.

 

Step 9.

The two texts, which follow describe two plants for generating electricity from wave power. Note the similarities and differences between the plants.

WAVE POWER.

 

This prototype wave-power plant on the Scottish island of Islay was constructed by building a concrete water column across a natural gully on the shoreline. Waves flowing in and out of the gully cause water in the column to move up and down. As the water moves up it compresses the air above and forces it through a wide tube at the back of the water column. As the water moves down air is drawn into the water column. The moving air passes through a turbine coupled to a generator. Both the turbine and generator are unusual. The turbine is a Wells turbine (named after its inventor) that keeps turning in one direction even though the air flow is constantly changing direction. It has two rotors, each with four blades.

The generator is a wound rotor induction motor, which acts as a generator when it is turning at speeds greater than 1,500 rpm. Below that speed it operates as a motor and takes power from the grid. This motor/generator is used because the turbine takes some time to build up to a speed where it can generate electricity. When the turbine slows down due to a lull in wave activity, the generator becomes an electric motor and keeps the turbine running at a minimum speed so that it is ready to accept the power from the next batch of waves.

The plant is controlled by a computer. It includes a PLC (programmable logic controller), which monitors the operation of the motor/generator and the amount of electricity going to or being taken from the grid. There is also testing equipment to monitor how much electricity the plant is producing and the efficiency of the water column, turbine, and generator.

This experimental plant generates 150 kW. Plans have been approved for the construction of a 1 MW.

Sources scheme: Adapted from Inside out; Wave power; Education Guardian.

 

High hopes for wave power project

The worlds first power station in the open sea is to be stationed off do unreal in Scotland. The machine, called Osprey (Ocean Swell-Powered Renewable Energy), will stand in 18 meters of water a kilometer out and not only harvest the larger waves, which produce higher outputs, but also gain power with waves from any direction. The device is known as an oscillating water column. As a wave rises, air is pushed through an air turbine and sucked back again as the wave falls.

The turbine has been designed by Professor Alan Wells, of Queens University, Belfast. It will generate 2 megawatts. There is potential for 300 Ospreys in Scottish waters, which could provide 10 percent of the countrys peak electricity demand.

 

LESSON 7.

SUMMARY OF IMPORTANT FACTS.

Principles of Electricity

 

A chemical element is built up from atoms. Each atom is made up of

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