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1) The new transformer requires general overhaul.
2) Since electrons are negative charges, they fly to the plate only when the plate is positive.
3) Most of the world's electric power is generated in steam plants driven by coal, oil,
nuclear energy, or gas.
2. , , .
1) College-level physics books describe a less misleading method of measuring electric energy flow.
2) It will be a new energy conservation system.
3) There is a certain amount of the radio-frequency energy.
3.
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1) The longer the wire, the greater is its resistance to a current flow.
2) The differences of these two substances are more noticeable than their similarities.
3) The supermagnet creates a magnetic twice as strong as that from a conventional iron-core electromagnet.
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1) Our device was in operation for some 10 years.
2) No expansion takes place as the steam flows through the blading.
3) Any current can flow in this circuit.
5.
, ; .
1) Heat changed water into vapour.
2) Tomorrow the representative of our company will test the ordered device.
3) When does mutual inductance take place?
6.
2 .
Conductivity
Current may pass through solid conductors, liquids, gases or any combination of these. Some substances like metals, for example, conduct electricity easily. Such substances as copper, silver, aluminum carry an electric current very well. They have very low resistance. Other substances, like rubber, glass, porcelain conduct electricity poorly. They have an extremely high resistance. The ability of a conductor to pass electric charges is called conductance or conductivity.
The opposition which a material offers to the flow of current is known as resistance. If the opposition is small, conductivity is good and the body is classed as a conductor. When resistance is high, conductivity is poor, and the substance is classed as a poor conductor or a good insulator. Thus, the greater conductivity a substance has, the less is its resistance. So we can say that conductivity is inversely proportional to resistance. The best conductor has the least resistance; quite opposite, the poorest conductor has the greatest resistance. Conductance depends upon four things, namely: the material of a conductor, its length, diameter and its temperature.
There is a great difference in conductance of various substances. All metals conduct current easily, but copper carries current more easily than iron, and silver is the best conductor. Therefore, silver has a greater conductance than copper.
The unit used for measuring conductivity is the siemens. Resistance and conductors are related. Conductance is I divided by resistance and vice versa:
Resistance = I / conductance
7.
:
1. Do all substances conduct electricity?
2. What materials conduct an electric current well?
3. What is conductance?
4. What property of a substance is the opposition to conductance?
5. What is the relation between resistance and conductance?
6. Which conductor carries current more readily?
8. , ? , :
Conductance depends upon three things, namely: the material of a conductor, its diameter and its temperature.
B 2
1
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1) A low-pass filter consists of an inductance coil and a condenser.
2) What factors does conductivity depend upon?
3) The ohmmeters readings are incorrect.
2. , , .
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1) The power station of a power system consists of a prime mover.
2) It has been necessary to find ways of reducing energy losses in power transmission lines.
3) Much of the Engine Department on board a ship concerns the maintenance of the ship.
3.
, , .
1) Copper is a better conductor that iron.
2) The specialty of an electrician is as interesting as the specialty of a radio-operator.
3) The more current passes through a resistor the higher is its temperature.
4.
, .
1) No current passes through the circuit.
2) There are some metal plates and insulators in a capacitor.
3) Are there any insulators?
5.
, ; .
1) Next time the temperature of the resistor will be much higher.
2) The engineers connected cells in parallel.
3) Do the readings on the scale show the value of voltage or resistance?
6.
2 .
Supermagnet
Scientists have achieved great success in the development of the first super strong superconducting magnet. For its size, weight, energy consumption it is the most powerful magnet ever built. Such magnets are used in dozens of laboratories throughout the world. The supermagnet creates a magnetic twice as strong as that from a conventional iron-core electromagnet. The new magnet runs from an ordinary automobile storage battery. The superconducting magnet produces a magnetic strength, or flux density, of 43000 gausses.
Scientists agree that such magnets can revolutionize almost every aspect of mans use of electricity including the generation, distribution and use of electric power. The new magnet is wound from a wire which is a superconductor. There are materials which have the remarkable property of losing all electrical resistance at temperatures near absolute zero. Once started, supercurrents of electricity flow through superconductors forever without loss in strength.
Until a few years ago superconductors were simply a laboratory curiosity. Scientists believed that strong magnets could not be made from them because the magnetism they create by their supercurrents destroys their superconductivity. But it was demonstrated that certain superconductors retain their properties even in strong magnetic fields.
The superconducting magnet contains a halfmile of very thin wire, about 5000 turns of wire, which are wound into a coil or solenoid. The coil is immersed in a vessel of liquid helium which keeps it at a temperature near 450ْ F.
The energy required to cool the coil is only a small fraction of that needed to create a comparable magnetic field with a standard electromagnet.
Essentially, therefore, the magnet produces almost all of its super magnetism for free.
7.
:
1. What is the difference between ordinary magnets and supermagnets?
2. Is the magnetic field created by the supermagnet and the ordinary magnet the same or different?
3. What flux density does the supermagnet create?
4. What is the new magnet wound from?
5. Where is the coil immersed into?
6. How is super magnetism produced by the supermagnet?
8. , ? , :
Most scientists are not sure that magnets can revolutionize almost every
aspect of mans use of electricity.
3
1.
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1) The high-pass filter passes currents of high frequencies and opposes the flow of
low frequency current.
2) The insulators are in good condition.
3) The regions main industry is oil production.
2.
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1) In this case a battery has a large current capacity.
2) The cell connection in parallel increases the current capacity.
3) The supply voltage varies with the load.
3.
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1) The shorter the wire, the less is its resistance to the current flow.
2) The ammeter is one of the most common meters.
3) This type of the circuits is more efficient one.
4.
, .
1) Some galvanometers detect and measure currents as small as 10ֿ¹¹ of an ampere per 1 mm of the scale.
2) No charges can move in an open circuit.
3) Any motion across the direction of the Faroe lines produces an e.m.f. in the conductor.
5.
, ; .
1) The readings on the scale will show the measured value of current.
2) The conductivity increased with heating.
3) A modern ship has a rather complex electrical equipment.
6.
2 .
Comparison of the A.C. and D.C. Circuits
In a d.c. circuit a current flows always in the same direction. In an a.c. circuit the supply terminals are continually reversing their polarity, so that the current so continual reverses its direction. In a d.c. circuit the voltage and the current being constant, there is no question of phase difference between the current and the voltage. But in a.c. circuits the e.m.f. and current are nut of phase wit each other.
A current setting up a magnetic flux surrounding the conductor in which it flows, important effects are observed in the a.c. The magnetic flux alternates with the current and induces an e.m.f. in the circuit. This e.m.f. gives rise to the phase difference between the current and applied voltage. In a.c. circuits capacitance effects may be important. A capacitor, when used in a d.c. circuit, constitutes after an initial charging an open circuit through which no current flews. But with an a.c. circuit the capacitor, being continually charged and discharged in opposite directions, takes a current and introduces "capacitance" into the circuit.
The a.c magnetic flux set up by .c. gives the possibility of using a transformer. It changes the voltage of the circuit as required. It is the major advantage of a.c. as compared with d.c. For the efficient transmissions of electric power over long distances, a high voltage is nss, the efficiency of transmission increasing with the increase of voltage. Since with d.c. it is much more difficult to increase the voltage, therefore the using of d.c. for transmission is limited.
With an a.c. supply a transformer can be used to transform the generated voltage to a high value, other transformers being used to step down this voltage.
7.
:
1. What is the direction of a d.c. (an a.c.)?
2. Why is there a phase difference between the current and voltage in an a.c. circuit?
3. When is an e.m.f. induced in the circuit?
4. What is the main advantage of an a.c.?
5. Which current (d. or a.) changes its voltage more easily?
6. What is the voltage of current changed by?
8.
, ? , :
Rather low voltage is nss for the efficient transmissions of electric power over long distances.
4
1.
. , , -s, , .. :
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- .
1) A transformer transfers electric energy from one electric circuit to another without a change in frequency.
2) We use different meters for different purposes.
3) Scientists agree that such magnets can revolutionize almost every aspect of mans use of electricity including the generation, distribution and use of electric power.
2.
, , .
1) Modern electric power systems use transformers to convert electricity into different voltages.
2) The cell connection in parallel increases the current capacity.
3) There are no energy storage facilities here.
3.
, , .
1) The best conductor has the least resistance; quite opposite, the poorest conductor has the greatest resistance.
2) That power station is the largest one in Ukraine.
3) The faster the change of current, the greater the e.m.f. that will he induced.
4.
, .
1) No current passes through that circuit.
2) Some resistors have a constant value - these are fixed resistors.
3) Any conductor can conduct current when high enough voltage is applied to it.
5.
, ; .
1) This engineer's experiment resulted in the design of new electric device.
2) The engineers will connect some additional elements to the circuit next time.
3) An electric cell consists of an electrolyte and two electrodes.
6.
2 .
Rectifiers
Most power sources supply a.c. because it is easily generated and transmitted over long lines. But d. currents are necessary for some industrial applications. Therefore it is frequently desirable to convert from a.c. to d.c. The most convenient way to change a.c. to d.c. is by means of a rectifier. A rectifier is capable of changing a.c. into d.c. The current thus changed is called "rectified".
The basic principle of a rectifier is that it permits current to flow in one direction only. A rectifier, a diode tube, is a device consisting of two elements, one being an electron emitter or cathode, the other an electron collector or anode or plate. Since electrons in a diode can flow in one direction only, from the cathode to the anode (plate), the diode provides the unilateral conduction necessary for rectification. Since electrons are negative charges, they fly to the plate only when the plate is positive.
When it becomes negative, it repels the electrons back to the cathode from which they were emitted. Therefore, when a. voltage is applied to the plate, it becomes alternately positive and negative so that plate current flows only during that half of the time when the plate (anode) is positive, and only in one direction. A diode tube operating in this manner cuts off the negative halves of the a.c. cycles and is called a half-wave rectifier. In the half-wave rectifier the current flows only during the positive half-cycle of the applied a.c. voltage.
The efficiency of the half-wave rectifier is low and it is used only for applications requiring a small current.
7.
:
1. What is an a.c. necessary to convert to a d.c. for?
2. What is a current changed by?
3. What is a rectifier?
4. What are the main parts of a rectifier?
5. What direction does a current flow in a rectifier?
6. What is the charge of the cathode (anode)?
8.
, ? , :
In the half-wave rectifier the current flows both during the positive and negative half-cycle of the applied a.c. voltage.
5
1.
. , , -s, , .. :
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- ;
- .
1) Last year we repaired our plants equipment.
2) What moves the coil and the pointer?
3) Electromagnets have wide application.
2.
, , .
1) A current flow produces some effects.
2) In that case a battery has a large voltage output.
3) When the current flow is decreased, the magnetic lines of force again cut the wire.
3.
, , .
1) The most convenient way to change a.c. to d.c. is by means of a rectifier.
2) The more experiments we carry out, the more data we obtain.
3) This meter is about three times as sharp as that one.
4.
, .
1) Are there any cells connected in series?
2) There are some models of diesel engines in that laboratory.
3) We used no very special devices to measure the value of resistance.
5.
, ; .
1) The radio station informed us about bad weather condition in the North Sea.
2) The real training of an electrical engineer begins on board ship.
3) Two parallel conductors forming an electric circuit will have a comparatively small self-inductance.
6.
2 .
Types of Inductance
An electric circuit, in which an e.m.f. is induced while a current is changing in this circuit, is called an inductive circuit and this circuit has, self-inductance. So the circuit, in which a change of current causes an e.m.f. to be induced within the circuit itself, possesses inductance or self-inductance. Self-inductance is the ability of a circuit to produce an e.m.f. in the same circuit in which the current is changing. Self-inductance is caused by variations in the magnetic field up by the varying current itself. Two parallel conductors forming an electric circuit will have a comparatively small self-inductance. But a solenoid will have a large self-inductance since there will be a considerable magnetic field linked with the solenoid.
When the e.m.f. is induced into a circuit by a change of flux, or in other wrds when the e.m.f. is produced by a current changing in an adjacent circuit, this property of a circuit is called mutual inductance.
Mutual inductance is the property of a circuit to produce an e.m.f. in a near-by circuit by induction when the current in the first circuit changes. The second circuit can also induce an e.m.f. in the first when the current in the second changes. Mutual inductance is the ability not only of the circuits but of coils as well. Mutual inductance is the common property of two associated electric circuits or two coils and is the same in both directions.
Both self-inductance and mutual inductance occur only when there is a change in current.
7.
:
1. When is an e.m.f. induced in a circuit?
2. What is self-induction?
3. What is self-inductance caused by?
4. What is mutual inductance?
5. When do two coils have mutual inductance?
6. Due to what is an e.m.f. induced in one of the two parallel coils?
8.
, ? , :
Only mutual inductance occurs when there is a change in current.
2
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) - Indefinite (Present, Past, Future).
2. can, may, must, to be able to, have to, to be to, should.
3. Participle I (Present Participle), Participle II (Past Participle) .
2.2. 2
1.
When are you planning to finish the
repair works. .
planning = Present Continuous Active to plan
2.
If painted the main engine will look better. ,
.
If painted Participle II
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3.
You will have to do it. .
2.3.
1
1
; - . . (b) .
) 1. The anode is attracting negatively charged ions.
2. The electrician has brought a repair list and some drawings to the dock master.
b) 1. The circuit elements are affected by many factors.
2. The shaft was connected to the motor by means of rigid coupling ().
2
; Participle 1 Participle 2 , . . , , -. .
1) While sailing in the Atlantic Ocean, the ship ran into a terrible storm.
2) 50 m3 of foam compound is also provided.
3) The state law applies to all tankers including those with double bottoms.
4) The pilot leading our ship through the channel is very experienced.
3
; . .
1) Current may pass through solid conductors, liquids, gases or any combination of these.
2) The magnitude of current can be measured.
3) Our company electricians should always take an active part in prevention of any electricity problems.
4) Then they will have to buy switches, batteries, bulbs, tubes, LEDs.
5) Heat losses were to be reduced constantly and effectively.
4
3 .
The Induced E.M.F.
A current flowing in a wire sets up a series of magnetic lines of force that surrounds the wire. When the current starts to flow, these lines of force jump out from the wire, cutting across the wire as they go out. A momentary e.m.f. is set up which is in opposition to the applied e.m.f. When the current flow is decreased, the magnetic lines of force again cut the wire. While the force lines are cutting the wire in the opposite direction, the induced e.m.f. is in the same direction as the applied e.m.f. If the current increases, the induced e.m.f. is directed opposite to it. If the current falls, it acts in the same direction as the current.
This e.m.f. will still be induced if the conductor is stationary and the magnetic field is moved so that the lines of force still out the conductor. It doesn't make any difference whether the magnetic field is stationary and the conductor moves or whether the conductor is stationary and the field moves. An e.m.f. is not induced in case a conductor moves parallel the force lines but only when it moves at an angle to these lines and outs them.
However, any motion across the direction of the Faroe lines produces an e.m.f. in the conductor. If this e.m.f acts in a closed circuit, current flows, if the circuit is open, the e.m.f. is still induced, but no current can flow since there is no closed circuit.
The induced e.m.f. depends upon the rate of flux change. The faster the change of current, the greater the e.m.f. that will he induced. The magnitude of the induced e.m.f. depends also upon the size and the shape of the wire and the strength of the magnetic field.
The induced e.m.f. and the current do not move along together, that is, in phase. When the current lags behind the induced e.m.f., this is called phase lag.
5
:
1. What is set up around a current carrying wire?
2. When do the force lines Jump out from the wire?
3. What does the induced e.m.f. depend upon?
2
1
; - . . (b) .
a) 1. We have improved one of the high-speed diesel engines.
2. Electromechanics is still solving a great number of problems.
b) 1. These wires are acted upon great overloads.
2. This scientist's discovery was followed by an intensive research work of others.
2
; Participle 1 Participle 2 , . . , , -. .
1) Being on board the training vessel, we practiced hard in seamanship.
2) The two new ships proposed will have the same dimensions.
3) The systems are intended for tankers and barges working between the West Coast and Alaska.
4) After leaving the condenser the liquid refrigerant () passes back to the regulator.
3
. . .
1) We had to substitute the bulb with the new one.
2) This cable is to be used for testing of the transmission line.
3) Scientists agree that such magnets can revolutionize almost every aspect of mans use of electricity including the generation, distribution and use of electric power.
4) One electric device may be larger than another one, but it may be less suitable.
5) These installations should be interconnected completing a single network.
4
2 .
Electrical Measurements
Electrical measurements are known to be used to measure both electrical quantities and non-electrical quantities by electrical methods. We know electrical measurements to be made by means of electric instruments. The measuring instruments are divided into indicating instruments and comparison ones. The accuracy and sensitivity of the latter are considered to be greater, but the actual comparison takes more time. The measuring with indicating instruments is stated to be faster and cheaper and so most measurements are performed by indicating instruments.
The electric measuring Instruments are calibrated in units of the quantity which they measure. The principles of operation of these instruments to measure various quantities vary widely, as do their forms of construction.
We say the measuring Instruments to be grouped into three main divisions. In the first category are rectifier instruments. The second category is known to include instruments whose indication depends on the square of the operating current.
The third category includes those instruments which are suitable for a.c. only. This class is considered to include the instrument operating on the induction principle, which are most commonly used as energy meters.
We find the use of electric measuring instruments to permit a whole series of important problems in modern technology to be solved by relatively simple means.
The USSR is known to produce all types of measuring instruments of the most modern construction.
5
:
1. What are electrical measurements used for?
2. What are electrical measurements made by?
3. What types are the measuring instruments divided into?
4. Which instruments (comparison or indicating) are used more often?
5. Are the principles of operation of all measuring instruments the same or different?
6. What instruments are there in the first category?
7. Why is the use of measuring instruments of great importance?
3
1
; - . . () .
a) 1. The engineers have chosen the step-down transformer for this purpose.
2) While the machinery is operating air gradually collects in the condenser.
b) 1. The testing of these indoor lines was followed by its wide employment.
2. Fire pumps are driven from the main engines.
2
; Participle I Participle II , . . , -. .
1) Approaching the port of London, we saw many various ships in the mouth of the Thames.
2) The methods used were found fruitful.
3) The vessel was towed into Cape Town.
4) When completed they will replace two of the existing tractor tugs at Tees.
3
; . .
1) Man-made satellites had to use solar cells as a source of power.
2) The elements of the circuits should be isolated by certain kind of fibres.
3) Power consumption can also be defined as a measure of comparison.
4) The electric field may be thought of as consisting of a number of lines of force.
5) You are to know the main principles of energy production.
4
2 .
The Principles of Meter Operation
It is important to have instruments by means of which we measure directly the quantity of certain factors such as: current, voltage, resistance.
Ammeters, voltmeters, ohmmeters are found to constitute the largest group of measuring Instruments These instruments are known to be called meters and they operate by measuring the various effects produced by the electric current.
They operate on the principle that a coil may be so placed in a magnetic field that it will tend to turn when a current flows in it. This turning action is known to be the principle of the electric motor. A meter is known to be a small electric motor. For everyday measurements indicating instruments are considered to be most convenient. They are known to have three essential parts: an operating mechanism, a controlling mechanism and a damping mechanism.
Types in common use for different purposes are: moving iron, moving coil, thermal, electrostatic and induction.
The moving coil instrument is found to be the most useful instrument. The principle on which it operates is that the force on a conductor in a magnetic field depends upn the current in the conductor. The magnetic field is provided by a small permanent magnet. A current-carrying coil has a magnetic field around it. If such a coil free to move is placed in another magnetic field, it will move due to the interaction between the two fields. When a current passes through the coil, an electromagnet is produced. The poles of the electromagnet are attracted by the poles of the permanent magnet and this moves the coil and the pointer.
5
:
1. What instruments constitute the largest group of the meters?
2. What principle do they operate on?
3. What is the main principle of a meter?
4. What are the main parts of an indicating instrument?
5. Which instrument is the most useful?
6. What is the principle of operation of a moving-coil instrument?
7. What does the permanent magnet provide?
4
1
; - . . () .
a) 1. The engineers have developed new type of DC generators.
2. The problem of the structure of matter is constantly occupying the minds of many scientists.
b) 1. The same kind of protection will be provided for auxiliary engines too.
2. The introduction of new fuses was followed by improving of operation of transmission power lines.
2
; Participle I Participle II , . . , , -. .
1) When sailing in thick fog, ships are obliged to give sound signals at regular intervals.
2) The main material used is castiron.
3) Fire pumps are driven from the main engines, giving a total Capacity of 6500 m3.
4) Approaching the vessel, we saw the flag of an English merchant ship on it.
3
; . .
1) The motor is to be connected to the pump by means of a bracket.
2) You should take into consideration safety precaution.
3) Every boiler must convert the chemical energy contained in the fuel in steam.
4) If the device is faulty you can not rely on its readings.
5) The heat from the nuclear chain reactor may be removed by the coolant.
4
2 .
Ohmmeters
Just as ammeters measure current and voltmeters measure voltage, ohmmeters are known to measure resistance. All ohmmeters have an internal source of power (usually a battery) which supplies a known voltage. The meter pointer deflection measures current and the scale is calibrated to read current in relation to voltage or resistance in ohms.
The basic principle of an ohmmeter is: a known voltage, supplied by a battery, is applied to an unknown resistance and the current is measured. It is evident from Ohm's law that when voltage and current are known, we can easily find resistance. As batteries age, their internal resistance increases, and their effective voltage output decreases. To compensate for the aging of batteries, a rheostat is placed in series with the meter. The rheostat is called zero-ohm control. An ohmmeter indicates zero when there is no resistance, but when the meter indicates infinity, there is maximum resistance.
There are three basic types of ohmmeters:
1. Simple series-type ohmmeter;
2. Shunt-type ohmmeter;
3. Voltage-divider ohmmeter.
In a series-type ohmmeter, as resistance increases, current decreases. Another type of ohmmeter is called a shunt-type ohmmeter because the resistor, being measured, is placed in shunt with the meter. The third type of meter is the voltage divider ohmmeter. The unknown resistance and the shunt-resistor form a voltage divider. When different values are inserted for unknown resistance, the voltage across the shunt-resistor will change, and in turn, the current through the meter will change. The series-type ohmmeter is known to be good for high ranges but the voltage divider is considered to be suitable for low ranges.
5
:
1. What is an ohmmeter used for?
2. What is the source of power in an ohmmeter?
3. What is the basic principle of an ohmmeter?
4. What types of ohmmeters are there?
5. What is a shunt-type ohmmeter?
5
1
; - . . () .
) 1) The engineers have refused from using these poor quality fuses.
2) Electricity is giving mankind efficient means for meeting the modern society requirements in energy.
b) 1) Today many highly conducting materials are produced on a massive scale.
2) This electric phenomenon was greatly influenced by these sets of external forces.
2
; Participle I Participle II , . . , , -. .
1) The chief engineer must give scantlings and drawings if required.
2) The amount of heat generated is very small.
3) The building of the first atomic power station was followed by the research work.
4) The pilot stood on the bridge giving orders to the helmsman.
3
; . .
1) Repairs can be executed without special shop equipment.
2) Nowadays power stations should be connected into power grids.
3) The current must be as small as possible not to melt the wires.
4) A fast reactor has to be designed to produce more fuel than it consumes.
5) Considerable development may be done in the energy industry.
4
2 .
The Principle of Transformer Action
A transformer is a simple device used in a.c. circuits for the purpose of changing voltage from one value to another. A transformer transfers electric energy from one electric circuit to another without a change in frequency. This energy transfer usually takes place with a voltage change. So transformers have to be generally used only with a.c.
A transformer may be defined s an apparatus without moving parts. It means that mechanical losses are entirely absent. The action of a transformer is based on electromagnetic induction. What does it mean? Each transformer has core on which the primary and the secondary are wound. The windings are linked magnetically.
The coil on which the a.c. is impressed on the input side of the transformer is called the primary, the one from which the induced e.m.f. is obtained on the output being known as the secondary. The coils may have air cores or they may be wound upon a laminated iron core. In the case of iron core transformers, the secondary voltage is very nearly equal to the primary voltage multiplied by the ratio of the number of the secondary to the number of the primary turns.
There is a limit to the frequencies that can be efficiently used in transformers with metallic cores. In case a very high frequency a.c. is used, air core transformers have to be used to eliminate core losses.
An a.voltage being applied to the terminals of the primary, the secondary is open-circuited. An a. magnetic flux is set up around the primary and this induces a back e.m.f. in the primary. A varying magnetic field is established between the two coils. The varying magnetic field will cut across the turns of the secondary and as the result of it an induced e.m.f. is produced across the secondary. This is the principle of a transformer action.
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1. What is the function of a transformer?
2. When does the energy transfer take place between two coils?
3. What current is used in a transformer?
4. Why are mechanical losses absent in transformers?
5. What are the main parts of a transformer?
6. What types of transformer cores are there?
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1) At present the nature of electrification is being explained by the electron theory.
2) These synchronous motors have been made to operate from a single-phase power source.
3) In some newer machines this reversal will be accomplished using power electronic devices, for example, diode rectifiers.
4) The first source of continuous current was produced by Volta.
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, that, one, it.
1) One should take into consideration that the energy sources of the world are decreased.
2) It is possible to carry out the repairs within the time.
3) This pull-push amplifier was introduced last year, and that one will be employed next four months.
4) One method of detecting the presence of a current in a wire is to measure the temperature rise in the wire.
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1) There is some force of attraction acting between the molecules of matter.
2) A two-winding transformer has two coils which have to be arranged so that the magnetic lines of force of one coil pass through the other one.
3) Both terminals of a generator are to be connected to the same pole of the current.
4) This material does not possess desired properties.
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1) Everybody knows this generator must operate continuously throughout the twenty four hours.
2) Solar power the scientists and engineers suggest to use is inexhaustible.
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1) To transmit a given amount of energy, less current is required at a high voltage than at a low voltage.
2) The circuit to be described will operate at high frequencies.
3) The magnetic flux is considered to be the result or effect due to the action of a magnetic force on a magnetizable body.
4) To simplify and make power generation cheaper the engineers will develop new type of energy generated installations.
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The Main Types of Transformers
Transformers may be classed according to the use they are designed for. Sometimes the transformer is used for operating a.c. ammeters, wattmeters and other measuring devices. Transformers may be used to make two electrical circuits electrically independent. But nearly all transformers come under one of the following classes: step-up and step-down transformers varying the ratio of turns between the primary and the secondary we can step up or step down the voltage. Some transformers are designed to raise the primary voltage to a higher value, such being known as step-up transformers. Others are constructed to reduce the primary voltage to a lower value, they are called step-down transformers.
A step-up transformer has more turns in the secondary than in its primary. In this type of transformer the current on the secondary side is lowered in the same ratio as the voltage is raised. In a step-down transformer there are fewer turns in the secondary than in its primary, the output voltage being smaller. In step-down transformers the current on the secondary side is raised in the same ratio as the voltage is lowered.
Transformers have many applications in a.c. circuits that require both the raising and lowering of the primary voltage well as the lowering and raising of the primary current.
There are transformers in which the number of turns in the secondary is the same as the number of turns in the primary. The secondary voltage is the same as the primary and this type of transformer is said to be a "one-to-one" transformer.
Transformers are widely applied in long-distance power transmission as well as in telephone, radio transmitters and receivers, television, electronic equipment. Transformers have a wide application on ships with different purposes. So as we have seen transformers are widely used in electrical engineering and they are of great importance.
7
:
1) What are transformers used for?
2) What are the main types of transformers?
3) According to what are transformers classed into step- up and step-down ones?
4) What is the main property of a step-down transformer?
5) What is "one-to-one" transformer?
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1) Transformers are being used to make two electrical circuits electrically independent.
2) The phenomenon which was discovered by Petrov was of the greatest importance.
3) Radioactive isotopes have been made in nuclear reactor.
4) The scientific researches will be followed by experimental work.
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1) It is proved that the electricity transporting can't be without any power losses.
2) The specialists find out that all the harmful affects of it can be easily eliminated.
3) One has to choose the insulating material that will be the most efficient and cheapest one.
4) It is the movement of electrons which constitutes an electric current.
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