Некоммерческое акционерное общество
АЛМАТИНСКИЙ УНИВЕРСИТЕТ ЭНЕРГЕТИКИ И СВЯЗИ
Кафедра иностранных языков
АНГЛИЙСКИЙ ЯЗЫК
Методические указания для развития навыков чтения и перевода текстов
(для студентов специальностей 5В071600 - Приборостроение)
Алматы 2012
Составитель: канд.филилог.наук, доцент У.Б.Серикбаева. Английский язык. Методические указания для развития навыков чтения и перевода текстов (для студентов специальностей 5ВО71600 – Приборостроение) – Алматы. АУЭС, 2012 -27 с.
Данные методические указания предназначены для применения на практических занятиях для студентов первого курса для развития навыков чтения и перевода текстов. Тексты взяты из оригинальной литературы. В каждом разделе имеются упражнения для закрепления лексики.
Рецензент: канд. тех. наук., доцент Сябина Н.В
Печатается по плану издания некоммерческого акционерного общества «Алматинский университет энергетики и связи» на 2012 г.
© НАО «Алматинский университет энергетики и связи», 2012 г.
Сводный план 2012. поз.262
Unit 1. Instrumentation
Instrumentation is a branch of science and technology, which is a branch of engineering that develops and manufactures instrumentation, processing and reporting, automatic and automated control systems. Instrumentation is a collection of instruments and their application for the purpose of Observation, Measurement and Control.
An instrument is a device that measures or manipulates variables such as flow, temperature, level or pressure. Instruments include many varied contrivances which can be as simple as valves and transmitters, and as complex as analyzers. Instruments often comprise control systems of varied processes. The control processes is one of the main branches of applied instrumentation.
The main direction of development is the instrument measuring equipment, consisting of methods and instruments for measurement of mechanical, electrical, magnetic, thermal, optical and other physical quantities. Measuring devices with automatic control and actuators form a technical basis of automated process control systems.
Instrumentation engineers is engaged in researching, developing, manufacturing technology and the exploitation of electronic devices in the workplace. Depending on the training may specialize in the design of power electronics devices, microprocessor – based information management and electronic equipment or develop a flexible automated production or design of analog and digital electronic measuring instruments (oscilloscopes, oscillators , phase meter) and devices functional, optical, solid –state and computer electronics.
Instrumentation engineer need to know the main trends and directions of the instrument – making techniques and technology of the industry, their relationship with relate industries, the basic fundamentals of programming languages and typical software solving scientific products aimed at solving scientific, engineering and technology, including information and measurement, instrumentation problems, basic elements and devices systems, processes and equipment, foundation design and analysis instruments and devices, including the stages of functional, engineering and technological design, requirements, standards and technical documentation, methods of feasibility studies of projects, production, marketing basics, the different classes of devices and systems, especially their design, production technology as well as conditions and methods of operation.
Professionally important qualities are:
Technical intelligence:
Logical thinking.
Creativity.
Spatial imagination.
Curiosity.
Ability of management activities.
The man who was educated specialist instrument will be in demand as an expert is always and everywhere, you will be at the forefront of technological progress. You will get the knowledge and skills to design, operate modern machinery controlled by computers and microelectronics, the design of electronic systems and programming.
Vocabulary notes:
To manufacture - производить
To measure equipment – измерить оборудование
Magnetic - магнитный
Thermal – тепловой
Quantity - количество
Actuators – приводить в движение
To be engaged in – заниматься чем-либо
To research - исследовать
To develop - развивать
To depend on – зависить от чего-либо
Power devices
Flexible - гибкий
Solid – твердый
To solve - решать
To require - требовать
Feasibility - выполнимость
Spatial imagination – пространственное воображение
Curiosity -редкость
To be in demand – быть востребованным
Forefront – центр
Exercise 1. Write the endings of the following sentences
1. Instrumentation is a …. of engineering that develops and …. Instrumentation.
2. Instrumentation engineer is ….. in ….. and the …. of electronic devices.
3. The main direction of development is the ….
4. Typical software products aimed at …. Scientific problems.
5.Professionally important qualities are : ……
Exercise 2. Answer the following questions
1. What is a instrumentation?
2. What is the main direction of instrumentation?
3. What do measuring devices form?
4. What should instrumentation engineer know?
5. What are professionally important qualities of engeneer?
Unit 2. Meters
Among the most common meters used there are ohmmeter, the ammeter and the voltmeter. The ohmmeter is used to measure the value of resistance. It consists of a milliameter calibriated to read in ohms, battery an resistors. The meter is connected in parallel and the circuit is not opened when its resistance is measured.
The ammeter is used to measure the value of current. When the ammeter is used the circuit should opened at one point and the terminals of the meter should be connected to it. One should take into consideration that the positive terminal of the meter is connected to the positive terminal of the source, the negative terminall – to the negative terminal of the source.
The ammeter should be connected in series
The reading on the scale show the
measured value.
Vocabulary notes
Meter
To measure
Value
In order to
Circuit
Capacity- мощность
Heat - нагревать
Rate- степень
To ptoduce – производить
To change
To vary
The more .. the more
Low
High
variable
Exercise 1.Complete the sentences using the correct variant
1.The ammeter is
a) a common meter.
b) an uncommon meter.
2.In order to measure the
a) the ohmmeter is used, value of current
b) the voltmeter is used.
c) the ammeter is used.
3.A meter has
a) positive terminals only.
b) negative terminals only.
c) positive and negative terminals.
4.When the ammeter is used
a) the circuit should be opened.
b) the circuit should not be opened.
5.One should take into consideration that
a) the positive terminal should be connected to the negative terminal.
b) the positive terminal should be connected to the positive terminal of the source.
Exercise 2. Complete these sentences using while. Follow the model
Model: The ammeter is used to measure the value of current....
The ammeter is used to measure the value of current while the ohmmeter is used to measure the value of resistance.
1.The ohmmeter is used to measure the value of resistance
2.The ammeter is connected in series
3.When the ammeter is used to measure the value of current the circuit should be opened
Exercise 3. Ask these questions to your groupmate
1.What is the ammeter used for?
2.What is the voltmeter used for?
3.What is the ohmmeter used for?
4.What terminals does a meter have?
5.Should the measured circuit be opened when the voltmeter is used?
6.Should the measured circuit be opened when the ammeter is used?
7.In what way should the voltmeter be connected to the circuit?
8.In what way should the ammeter be connected to the circuit?
9.What is the difference between a voltmeter and an ammeter?
10.What common meters are used to measure the values in a circuit?
Exercise 4. Solve the following problems
1.Suppose the ammeter scale reads 1.9 amp, the voltmeter scale reads 2.4 V; how much is the value of resistance in the measured circuit?
2.Suppose the ohmmeter scale reads 75 ohms, the voltmeter scale reads 220 V; how much is the value of current in the measured circuit?
3.Suppose that you have a series circuit consisting of three resistors and a voltage source. Ri = 0.18 ohm, R2= 1.15 ohms, R.3 = 2 ohms, 1=10 amp. Find the voltage drop across each resistor; find the value of voltage in the circuit. Suppose R( gets open. What does it result in?
4.Two resistors are connected in series. Ri = 7,000, R2= 2,200, 1 = 110 amp. Find the voltage drop across each resistor. Suppose no current passes through the circuit, what does it result from?
Exercise 5. Translate into Russian using чем ... тем
1.The more one studies nature, the better one knows its laws.
2.The longer one learns, the more one knows.
3.The higher the atmosphere, the less is its pressure.
4.The heavier the object, the more work one has to do in order to lift it.
5.The greater the number of free electrons in any metal, the higher is its conductivity.
Exercise 6. Translate into Russian. Mind no
1.There is no energy in this machine.
2.No charges move through an open circuit.
3.No material is a perfect conductor of electricity.
4.No electric machinery is used without protection.
5.No special material is needed in this case.
A resistor is one of the most common elements of any circuit. Resistors are used:
1.to reduce the value of current in'the circuit
2.to produce IR voltage drop and in this way to change the value of the voltage.
When current is passing through a resistor its temperature rises high. The higher the value of current the higher is the temperature of a resistor.Each resistor has a maximum temperature
Each resistor has a maximum temperature to which it may be heated without a trouble.
If the tempe rature rises higher the resistor gets open and opens the circuit.
Resistors are rated in watts. The watt is the rate at which electric energy is supplied when a current of one ampere is passing at a potential difference of one volt. A resistor is rated as a 1-W resistor if its resistance equals 1,000,000 ohms and its current-carrying capacity equals 1/1,000,000 amp, since P = E x I = IR x I = I2R where P - power is given in watts, R - resistance is given in ohms and I - current is given in amperes.
If a resistor has a resistance of only 2 ohms but its current-carrying capacity equals 2,000 amp, it is rated as a 8,000,000-W resistor.
Some resistors have a constant value - these are fixed resistors, the value of other esistors may be varied - these are variable resistors.
Exercise 1. Complete the sentences using the correct variant
1.A resistor is used
a) to measure the resistance.
b) to reduce the current.
c) to change the resisistance
d) to produce IR voltage drop.
2.When current passes through a resistance
a)its temperature drops
b)its temperature rises.
3.Resistor are rated
a) in ohms
b)in volts
4.Power is given
a) in amperes
b) in watt
5. fixed resistor have
a) a constant value
b) a variable value
6.The value of a variable resistor
a) is fixed.
b) is varied.
7. The higher the value of current,
a) the lower is the temperature of a resistor,
b) the higher is the temperature of a resistor
Exercise 2. Ask these questions to your groupmate
1.What is a resistor used for?
2.When does the temperature of a resistor rise?
3.What element is used to change the value of voltage?
4.How are resistors rated?
5.What types of resistors do you know?
6.When does a resistor get open?
7.What does an open resistor result in?
8.What is the difference between a fixed resistor and a variable resistor
9.How much is the current-carrying capacity of a two-ohm resistor?
10.What resistors have a variable value?
A capacitor is one of the main elements of a circuit. It is used to store electric energy. A capacitor stores electric energy provided that a voltage source is applied to it.
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Figure8 Figure 9
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The main parts of a capacitor are metal plates and insulators. The function of insulators is to isolate the metal plates and in this way to prevent a short.
In the diagram one can see two common types of capacitors in use nowadays: a fixed capacitor and a variable one. The plates of a fixed capacitor cannot be moved; for this reason its capacity does not change. The plates of a variable capacitor move; its capacity changes. The greater the distance between the plates, the less is the capacity of a capacitor. Variable capacitors are commonly used by radiomen; their function is to vaiy the frequency in the circuit. Fixed capacitors are used in telephone and radio work.
Fixed capacitors have insulators produced of paper, ceramics and other materials; variable capacitors have air insulators. Paper capacitors are commonly used in radio and electronics; their advantage is their high capacity: it may be higher than 1,000 picofarad.
Besides, electrolyte capacitors are highly in use. They also have a very high capacity: it varies from 0.5 to 2,000 microfarad. Their disadvantage is that they change their capacity when the temperature changes. They can operate without a change only at temperatures not lower than -40° С.
Common troubles in capacitors are an open and a short. A capacitor stops operating and does not store energy in case it has a trouble. A capacitor with a trouble should be substituted by a new one.
Vocabulary notes
Capacitor - конденсатор
To store- сохранить
Insulator –изолятор
Frequincy - частота
Distance –расстояние
Advantage – преимущество
Disadvantage -недостаток
Plate –анод (лампы)
Part -часть
To apply –прилагать применять
To move – двигаться
To prevent -предотвратить
Reason -причина
For this reason- по этой причине
Besides- кроме того
Provided that - при условии что
Exercise 1. Complete these sentences using the correct variant
1.A capacitor is used
a) to supply voltage.
b)to increase the voltage output.
c)to store energy.
2.The main parts of a capacitor are
a) insulators only
b)metal plates only.
c)metal plates and isulotors between them
3.The function of insulators is
a) to store energy
b) to isolate the metal plates
c) to prevent a short between the metal plate
4. the capacity depends on
a) the size of the plates
b) the distance between the plates
c) the material of the insulators
5.The capacity of a fixed capacitor
a) is constant
b) is varied
6.The plates of a variable capacitor
a) can be moved
b) cannot be moved
7. In order to charge a capacitor a voltage source is applied
a) to the metal plates
b) to the insulators
8.The greater the distance between the plates
a) the greater is the capacity of a capacitor
b) the less is the capacity
9. Variable capacitors have
a) air insulators
b)paper insulators
c) ceramic insulators
10. Electrolyte capacitors have
a) a very low capacity
b) a very high capacity
11. In case a capacitor has a trouble
a) it operates
b) it stops operating
Exercise 2. Complete these sentences
1.The plates of a fixed capacitor cannot be moved to vary the capacity….
2. The capacity of a variable capacitor is varied ….
3. Electrolyte capacitors change their capacity when the temperature changes….
4. The less the distance between the plates, the greater is the capacity….
5. When a capacitor has no trouble it stores energy…
Exercise 3. Ask these questions to your groupmate
1.What is a capacitor used for?
2.What are the main parts of a capacitor?
3.What is the function of insulators?
4.What does the capacity of a capacitor depend on?
5.What is the difference between a fixed capacitor and a variable one?
6.What should be done in order to change a capacitor?
7.What is the relation between the value of capacity and the distance of plates?
8.What type of insulators have variable capacitors?
9.What should be done in case a capacitor has a trouble?
Exercise 4. Solve these problems
Draw a diagram of a circuit consisting of two resistors and two capacitors
connected in parallel. A battery of four cells is applied to the circuit. Two ammeters are used: one is connected to the main line, the other - to a parallel branch. What is the function of each element? In what way can one increase the value of resistance in the circuit?
Suppose one of the branches stops operating. What does it result from?
Unit 5. Conductors and Insulators
Conductors are materials having a low resistance so that current easily passes through them. The lower the resistance of the material, the more current can pass through it.
The most common conductors are metals. Silver and copper are the best of them. The advantage of copper is that it is much cheaper than silver. Thus copper is widely used to produce wire conductors. One of the common functions of wire conductors is to connect a voltage source to a load resistance. Since copper wire conductors have a very low resistance a minimum voltage drop is produced in them. Thus, all of the applied voltage can produce current in the load resistance.
It should be taken into consideration that most materials change the value of resistance when their temperature changes.
Metals increase their resistance when the temperature increases while carbon decreases its resistance when the temperature increases. Thus metals have a positive temperature coefficient of resistance while carbon has a negative temperature coefficient. The smaller is the temperature coefficient or the less the change of resistance with the change of temperature, the more perfect is the resistance material.
Materials having a very high resistance are called insulators. Current passes through insulators with great difficulty.
The most common insulators are air, paper, rubber, plastics.
Any insulator can conduct current when a high enough voltage is applied to it. Currents of great value must be applied to insulators in order to make them conduct. The higher the resistance of an insulator, the greater the applied voltage must be.
When an insulator is connected to a voltage source, it stores electric charge and a potential is produced on the insulator. Thus, insulators have the two main functions:
1) to isolate conducting wires and thus to prevent a short between them and
2) to store electric charge when a voltage source is applied.
Exercise 1. Find answers to these questions in the text above
1.What materials are called conductors?
2.What is the advantage of copper compared with silver?
3.What is the most common function of wire conductors?
4.Why is a minimum voltage drop produced in copper conductors?
5.What is the relation between the value of resistance and the temperature in carbon?
6.What materials are called insulators?
7.What are the most common insulators?
8.What are the two main functions of insulators?
Exercise 2. Complete the sentences using the correct variant
1.Current passes through conductors
a) easily
b) with great difficulty
2.Copper and silver are
a) low resistance.
b) high resistance.
3.Air, paper and plastics are
a) common insulators.
b) common conductors.
4.In case a high voltage is applied to
a) it does not conduct current
b) it conducts current
5.Insulators are used
a) to store electric charge
b) to reduce voltage
c) to prevent a short between conducting wires
6.Metals increase their resistance
a)when the temperature decreases.
b)when the temperature increases.
7.Metals have
a) a positive temperature coefficient of resistance
b) negative temperature coefficient of resistance.
Exercise 3. Put questions in italics
1.Conductors have a low resistance
2.Current passes through insulators with great difficulty
3.Metals are common conductors
4.To make insulators conduct, currents of great value must be applied
5.Carbon decreases its resistance when the temperature increases ....
6.Metals have a positive temperature coefficient of resistance ....
Exercise 4. Ask these questions to your groupmate
1.What is the difference between conductors and insulators?
2.How does current pass through insulators?
3.What materials are commonly used to produce insulators?
4.What materials are commonly used to produce conductors?
5.In what case do insulators conduct current?
6.How does resistance change when the temperature decreases?
Vocabulary notes
core сердечник
winding [’waindig] обмотка
turn виток
to step up повышать
to step down понижать
frequency ['friikwansi] частота
due to [‘dju: ta] благодаря, из-за
Exercise 5. Put down the Russian for
iron core __________ primary winding
closed core ________ secondary winding
input voltage ________ step-up transformer
output voltage ______ step-down transformer
A transformer is used to transfer energy. Due to the transformer electric power may be transferred at a high voltage and reduced at the point where it must be used to any value. Besides, a transformer is used to change the voltage and current value in a circuit.
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Figure 10 Figure 11 |
A two-winding transformer consists of a closed core and two coils (windings). The primary winding is connected to the voltage source. It receives energy. The secondary winding is connected to the load resistance and supplies energy to the load.
The value of voltage across the secondary terminal depends on the number of turns in it. In case it is equal to the number of turns in the primary winding the voltage in the secondary winding is the same as in the primary.
In case the secondary has more turns than the primary the output voltage is greater than the input voltage. The voltage in the secondary is greater than the voltage in the primary by as many times as the number of turns in the secondary is greater than the number of turns in the primary. A transformer of this type increases or steps up the voltage and is called a step-up transformer. In case the secondary has fewer turns than the primary the output voltage is lower than the input. Such a transformer decreases or steps down the voltage, it is called a step-down transformer.
Compare T\ and Ti in the diagram. T\ has an iron core. For this reason it is used for low-frequency currents. Ti has an air core and is used for high frequencies.
Common troubles in transformers are an open in the winding, a short- between the primary and the secondary, and a short between turns. In case a transformer has a trouble it stops operating or operates badly. A transformer with a trouble should be substituted.
Exercise 1. Complete the sentences using the correct variant
1.A transformer is used
a) to store energy
b)to prevent the change of energy.
c)to transfer energy.
d)to change the voltage and current value in a circuit
2.Electric power is transferred at a high voltage and reduced to any value.
a)due to resistors
b)due to capacitors
c) due to tranformers
3.A transformer consists of
a)cores only
b) the primary and the srcondary windings
c) a core and the primary and the secondary windings
4.The function of the primary is
a) to prevent the change of voltage.
b)to supply energy.
c)to receive energy.
5.The function of the secondary is
a) to receive energy
b) to supply energy.
c)to transfer energy
d)to decrease the value of charge.
6.A step-up transformer is used
a) to step down or decrease the secondary voltage
b)to step up or increase the primary voltage.
7.A step-down transformer is used
a) to step down the secondary voltage,
b) to step down the primary voltage.
8.A transformer with an
a) is used for high-frequency currents, iron core
b) is used for low-frequency currents.
9. A transformer with an air
a) for high-frequency current s and for low- core is used frequency currents.
b) for high-frequency currents only.
10. In a step-up transformer
a) the number of turns of the secondary winding is greater than the number of turns of the primary,
b) the number of turns of the primary winding is greater than the number of turns of the secondary.
11. A transformer should be
a) in case it has an open in the winding, substituted
b) in case it has a short between the primary and the secondary,
c) in case it has a short between turns.
Exercise 2. Put questions in italics
1.The secondary winding of a transformer is connected to the load resistance .
2.The primary winding receives energy .
3.A step-down transformer decreases the primary voltage .
4.An air core transformer is used for high-frequency currents
5.In a step-up transformer the number of turns of the secondary winding is greater than the number of turns of the primary winding.
Exercise 3. Ask these questions to your groupmate
1.What is a transformer used for?
2.What does a transformer consist of?
3.What is the function of the primary winding?
4.What is the function of the secondary winding?
5.What type of transformer is called a step-up transformer?
6.What type of transformer is used for high-frequency currents?
7.What type of transformer is called a step-down transformer?
8.What type of transformer is used for low-frequency currents?
9.What is the relation between the number of turns in the windings and the value of current?
10.What are common troubles in a transformer?
11.What should be done in case a transformer has a trouble?
Exercise 4. Read about current transformers. Answer the questions that follow
Current transformers are used for operating ammeters, wattmeters, and other measuring devices. They produce in the meters a current lower than the measured current but proportional to it.
Current transformers also insulate the instrument from the circuit which is being measured. This is necessary for high voltage circuits.
1.What is a current transformer used for?
2.What type of current does it produce?
Electromagnetic Relay
Electricmagnetic devices called relays are widely used in various branches of industry.
The main parts of a relay are an electromagnet, a spring and an armature. When a current atarts flowing in the electromagnetic winding, the armature moves and the spring closes the contacts. The primary circuit of a relay is its electromagnetic circuit and the secondary circuit is the one closed by the contacts.
When there is no current in the relays primary circuit, the spring pulls the armature and the contacts open. A relay is used to control the work of an electric motor. The relay is placed close to the motor which is connected to its secondary circuit. The armature closes the contacts of the secondary circuit, and the more starts opening, it will stop when the relay opens.
Without a relay,conductors with a large cross-section would have to be brought to the motor. This would be very uneconomical. The current in a relay is tens and even thousands of times smaller than that used to power the motor. Therefore, the connecting wires can have small cross-sections.. in many sustems the relay primary ciecuit operates automatically. Every evening and morning street lights are switched on and off from the main control panel by means of a greatt number of relays.
Vocabulary notes
Fuse- плавкий предохранитель
Link – звено связь
Fault- дефект неисправность
Faulty- неисправный
Equipment -оборудование
Installation –установка
To protect –защищать предохранять
To utilize- использовать
To equip - оборудовать
To serve -служить
To melt- плавить
Up to – вплоть до
Exercise 1. Complete the sentences using correct variant
1.The main parts of a relay are
a)an electromagnetic, a capacitor, and a spring
b) an electromagnetic , an armature, and a spring
2. When current starts
a)the spring opens he contacts, flowing
b)the spring closes the contacts
3.the spring pulls the
a) when there is current in the primary circuit, armature
b) when there is no current in the primary curcuit
4. the wires connecting
a) have a large cross-section, the panel with the relay
b)have a small cross- section
5, street lights are
a)by means of relays, switched on and off
b)by means of electric motors
Exercise 2. Put questions in italics
1.The primary circuit of a relay is its electromagnetic circuit
2.When there is no current in the relays primary circuit the contacts open
3.Without a relay conductors with a large cross- section be used.
4. Every evening street ligts are swoitched on
Exercise 3. Answer the following questions
1. What are the main parts of a relay?
2. How is relay put into operation?
3. When does the spring pull the armature?
4. What wires connect the panel with the relay?
5. By what means are street lights switched on and off?
Exercise 4. Find correct answer
1. In what position does the switch have high or low resistance?
2. What are the main function of the switch?
3. In what position is the switch open or closed?
4. In what way is the switch connected to the circuit?
a) Switches are used to open and close the circuits
b) closed is the on position, open is the off-position
c) the switch is connected in series with the load
d) in the on-position the closed switch hs a very low resistance, which results in maximum current in the load with zero voltage loss across the switch, When the switchis off it has a very high resistance and no current flows through the circuit.
Exercise 5. Translate into Russian. Mind both…. and, in case, up to
1. Both solid and gaseous insulators are highly in use
2. in case a fuse gets faulty it should be replaced by a new one.
3. capacitors of very gihg capacity – up to 1000 and more mF – are utilized in modern insulators
Unit 8. Electric Motors
Motors are used for converting different forms of energy into mechanical energy.The main part of a motor is a coil or armature. The armature is placed between the poles of a powerful magnet. When a motor is putinto operetion current starts flowing through the coil (srmature) and the armature starts rotaning.
Electric motors are used practically in every branch of industry, transport and agriculture. Naturally they are produced in many different designs. They are used in undustrial plants and operate under different conditions.
Each motor is supplied with a nameplate which bears machine ratings: output power, voltage, the rated current, the starting current. The power factor, the efficiency and the rated torgue.
The motor ratings should be taken into considiration since they are necessary for the users. On them depends the length of motors service life, which is normally equal to about 10 uears, provided that the operating conditions are normal. Naturally, under abnormal conditions the service life becomes much shoter: motors operate poorly and may have different faults.
Vocabulary notes. Read and translate these words
To convert
Coil
Pole
Rotate
Supply
Nameplate
Bear
Rate
Torque
To take into considiration
Equal
Abnormal
fault
Exercise 1. Complete the sentences using the correct variant
1. Motors are used
a) for transmitting energy
b) for converting energy
2. Motors main part is
a) the frame
b) the armature
c) the stator
3. the armature is placed
a) between the poles of the magnet
b) about the poles of the magnet
4. Motors service life becomes
a) under normal conditions, shorter
b) under abnomal conditions.
5. faulty motors operate
a) normally
b) poorly
Exercise 2. Ask these questions
1. What are motors used for?
2. What is the motors main part?
3. Where is the armature placed?
4. What ratings do the nameplate of a motor bear?
5. Under what conditions does a motor operate mormally (poorly)?
Unit 9. Electric current
Electric current is a flow of electric charge through a medium. This charge is typically carried by moving electrons in a conductor such as wire. It can also be carried by ions in an electrolyte, or by both ions and electrons in a plasma. The SI unit for measuring the rate of flow of electric charge is the ampere, which is charge flowing through some surface at the rate of one coulomb per second. Electric current is measured using an ammeter.
The conventional symbol for current is I, which originates from the French phrase intensite de courant, or in English current intensity. This phrase is frequently used when discussing the value of an electric current. The I symbol was used by Andre-Marie Ampere after whom the unit of electric current is named, in formulating the eponymous Ampere”s force law which be discovered in 1820. The notation travelled from France to England, where it became standard, although at least one jounal did not change from using C to I until 1896.
In metallic solids, electricity flows by means of electrons, from lower to higher electrical potential. In other media, any stream of charged objects may constitute an electric current. To provide a definition of current that is independent of the type of charge carriers flowing, conventional current is defined to flow in the same direction as positive charges. So in metals where the charge carriers (electrons) are negative, conventional current flows in the opposite direction as the electrons. In conductors where the charge carriers are positive, conventional current flows in the same direction as the charge carriers.
In vacuum, a beam of ions or electrons may be formed. In other conductive materials, the electric current is due to the flow of both positively and negatively charged particles at the same time. In still others, the current is entirely due to positive charge flow. For example, the electric currents in electrolytes are flows of positively and negatively charged ions. In a common lead- acid electrochemical cell, electric currents are composed of positive hydrogen ions (protons) flowing in one direction and negative sulfate ions flowing in the other. Electric currents in sparks or plasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, the electric current is entirely composed of flowing ions. In a semiconductor it is sometimes useful to think of the current as due to the flow of positive “holes” (the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron). This is the case in a p-type semiconductor.
Vocabulary notes
Flow - поток
Charge - заряд
Wire - провод
Electrolyte - электролит
Plasma -плазма
Rate of flow – уровень потока
Ammeter - амперметр
Current intensity – интенсивность тока
Eponymous
Notation
Solid - твердый
Stream
Beam of ions – ионный луч
Lead – acid
Sulfate
Sparks
Holes
Exercise 1. Put these questions to your groupmate
1. What is electric current?
2. What is electric charge carried by?
3. What does electric current use to measure?
4. What is the conventional symbol for current?
5. Where a beam of ions or electrons may be formed?
Exercise 2. Complete these sentences using the words from the text
1. Electric current can be carried by … in an ….
2. In metallic …, electricity flows by means of electrons.
3. Conventional current is defined to … in the same direction as positive charges.
4. Electric currents in … or … are flows of electrons as well as positive and negative ions.
5. Electric current is entirely composed of … ions.
Unit 10. Metals
A solid conductive metal contains mobile or free electrons, originating in the conduction electrons. These electrons are bound to the metal lattice but no longer to an individual atom. Even with no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there is zero net current within the metal. Given a surface through which a metal wire passes, electrons move in both directions across the surface at an equal rate. As George Gamow said “ the metallic substances differ from all other materials by the fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what call an electric current.”
When a metal wire is connected across the two terminals of a DC voltage source such as a battery, the source places an electric field across the conductor. The moment contact is made; the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electrons are therefore the charge carrier in a typical solid conductor.
Vocabulary notes
Solid- твердый
Conduction
Lattice – решетка
Randomly –случайно
On average –в среднем
Net current – чистый ток
Equal rate – равная норма
Fill up - наполнять
Unattached -непривязанный
Aimlessly –безцельно
Exercise 1. Complete these sentences with the words from the text
1. A… conductive metals contains mobile or free …..
2. These… move about …. Due to the therminal energy.
3. The interior of a metal is …. with a large number of … electrons.
4. Free electrons… in the direction of the force.
5. Free electrons of the conductor are forced to drift toward the positive terminal under the ….. of this field.
Supplementary readings
Text 1. Electrolytes
Electric currents in electrolytes are flows of electrically charged particles. For example, if an electric field is placed across a solution of Na and CI the sodium ions move towards the negative electrode (cathode), while the chloride ions move towards the positive electrode (anode). Reactions take place at both electrode surfaces, absorbing each ion.
Water – ice and certain solid electrolytes called proton conductors contain positive hydrogen ions or “protons” which are mobile. In these materials, electric currents are composed of moving protons, as opposed to the moving electrons found in metals. In certain electrolyte mixtures, brightly – coloured ions form the moving electric charges. The slow migration of these ions means that the current is visible.
Vocabulary notes
Sodium ions
Chloride ions
To absorb
Visible
Text 2. Gases and plasmas
In air and other ordinary gases below the breakdown field, the dominant sources of electrical conduction is via relatively few mobile ions produced by radioactive gases, ultraviolet light, or cosmic rays. Since the electrical conductivity is low, gases are dielectrics or insulators. However, once the applied electric field approaches the breakdown value, free electrons become sufficiently accelerated by the electric field to create additional free electrons by colliding, and ionizing, neutral gas atoms or molecules in a process called avalanche breakdown. The breakdown process forms a plasma that contains enough mobile electrons and positive ions to make it an electrical conductor. In the process. It forms a light emitting conductive path, such as a spark, arc or lightning.
Plasma is the state of matter where some of the electrons in a gas are stripped or ionized from their molecules or atoms. A plasma can be formed by high temperature, or by application of a high electric or alternating magnetic field as noted above. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than the heavier positive ions, and hence carry the bulk of the current.
Vocabulary notes
Breakdown field
Approach
Breakdown value
Colliding
Avalanche
Emitting
Conductive path
Spark
To strip
Bulk
Text 3.Vacuum
Such a “perfect vacuum” contains no charged particles, it normally behaves as a perfect insulator. However, metal electrode surfaces can cause a region of the vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission. Thermionic emission occurs when the thermal energy exceeds the metals work function, while field election emission occurs when the electric field at the surface of the metal is high enough to cause tunneling, which results in the ejection of free electrons from the metal into the vacuum. Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes.
Cold electrodes can also spontaneously produce electron clods via thermionic emission when small incandescent regions (called cathode spots or anode spots) are formed. These are incandescent regions of the electrode surface that are created by a localized high current flow. These regions may be initiated by field electron emission, but are then sustained by localized thermionic emission once a vacuum are forms. These small electron – emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field. Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conductivity.
Vocabulary notes
Insulator
To cause
Conductive
To inject
Electron emission
Thermionic emission
To occur
Exceed
Surface
Tunneling
Ejection
Heated
To generate
Electron loud
Filament
Heated cathode
Tubes
Spontaneously
Incandescent regions
Cathode spots
Anode spots
Localize
Current
To be initiated
Sustained
Electron-emitting regions
Explosively
Sprytrons
Switch
Amplifying
Text 4. Electromagnetism
According to Ampere”s law, an electric current produces a magnetic field. Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.
Electric current can be directly measured with a galvanometer, but this method involves breaking the electrical circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices used for this include Hall effect sensors current clamps, current transformers, and Rogowski coils.
The theory of Special Relatively allows one to transform the magnetic field into a static electric field for an observer moving at the same speed as the charge in the diagram. The amount of current is particular to a reference frame.
Vocabulary notes
Pattern
Circulate field
Surrounding
Wire
Measure
Galvanometer
Break
Inconvenient
Detect
Associated
Device
Sensors
Current clamps
Current transformers
Coils
To allow
Amount
Text 5. Conventions
A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges or both, a convention for the direction of current which is independent of the type of charge carriers is needed. The direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges.
In metals, which make up the wires and other conductors in most electrical circuits the positive charges are immobile, and the charge carries are electrons. Because the electron carries negative charge, the electron motion in a metal conductor is in the direction opposite to that of conventional ( or electric) current.
When analyzing electrical circuits, the actual direction of current through a specific circuit element is usually unknown. Consequently, each circuit element is assigned a current variable with an arbitrarily chosen reference direction. When the circuit is solved, the circuit element currents may have positive or negative values. A negative value means that the actual direction of current through that circuit element is opposite that of the chosen reference direction. In electronic circuits the reference current directions are usually chosen so that all current flow toward ground. This often matches conventional current direction, because in many circuits the power supply voltage is positive with respect to ground.
Natural examples include lightning and the solar wind, the source of the polar auroras (aurora borealis and aurora australis). The artificial form of electric current is the flow of conduction electrons in metal wires, such as the overhead power lines that deliver electrical energy across long distance and the smaller wires within electrical and electronic equipment. In electronics, other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube, the flow of ions inside a battery or neuron and the flow of holes within a semiconductor.
Vocabulary notes: Translate and learn these words
Equal flow
Convention
Conductors
Immobile
Motion
Consequently
Vary
Reference direction
To solve
Value
To choose
Power supply
Respect to
Ground
Solar wind
Source
Polar auroras
Borealis
Artificial
Overhead power
Delive
Список литературы
1. Eric H. Glendinning. Electronics. London.1996
2. John McEwan. Power Engineering. Second edition. London. 1998
3. Oxford- Russian Dictionary.Oxford University Press. 1997
4. Steve Taelore-Knowles. Lazer. London.2008
5. David Cotton. Power Engineering.. London.2009
6. Simont Kent. Electronics. London. 2008
Содержание
Unit 1. Instrumentation 3
Unit 2. Meters 4
Unit 3. Resistors 7
Unit 4. Capacitors 8
Unit 5. Conductors and Insulators 10
Unit 6.Transformers 13
Unit 7. Current Transformers 15
Unit 8. Electric Motors 17
Unit 9. Electric current 18
Unit 10. Metals 20
Supplementary readings
Text 1. Electrolytes 21
Text 2. Gases and plasmas 21
Text 3.Vacuum 22
Text 4. Electromagnetism 23
Text 5. Conventions 23