10. Выделите в тексте элементы, которые, на ваш взгляд, несут важную информацию. Обсудите ваш выбор с одногруппниками.

11. оставьте логический план текста и на его основе, а также пользуясь ключевыми элементами из упражнения 7, расскажите об аккумуляторах.

/ устройств / процессов. Расскажите, что вы знаете о них. Опредепо формальным признакам часть речи выделенных в тек-

сте слов.

3. Прочтите и переведите текст.

ELECTRICAL MEASURING INSTRUMENTS

General Electrical Principles. To measure the magnitude of any phenomenon calls for the use of theДeffects produced by it. For the measurement of a mass, for example, we determine its weight; or we might utilize the force required to give it a certain acceleration. Again, for the measurement of temperature we use the expansion of solids, liquids, or gases, the change in electrical resistance of a wire, or the thermoelectromotive force produced at the junction ofИtwo conductors, etc. For the everyday measurement such indicating instruments are most convenient, in which the amount of the quantity to be measured is directly shown by the position of a pointer on a graduated scale or dial.

For the production of such instruments, some effect is employed which enables the phenomenon to be measured to produce a mechanical force tending to move the pointer along its scale; this is resisted by a controlling force which tends to move the index in the opposite direction, towards some zero position. The actual displacement of the index, or deflection, is the resultant of these two forces, and is greater the greater the magnitude of the deflecting force or of the phenomenon to be measured.

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As a matter of fact, one single principle is known to underlie all electromagnetic instruments, viz. that the current-carrying circuit tends to enclose as large a magnetic field as possible. In the moving needle galvanometers, the magnetic needle turns so that more of its lines or force pass

through the coil, while in the moving coil instrument the coil sets itself so Сas to enclose as much of the field of the magnet as possible. In the soft iron instruments, the iron moves so as to increase the magnetic flux produced by the coil, and in the dynamometer the moving coil turns so that its magnetic effect increases that of the fixed coil. Should the conducting circuit be made entirely of flexible material in a uniform field, it would become circular in order to enclose the maximum possible area, while, if the current flowed in a liquid conductor – such, for instance, as mercury – it would actually try to reduce its section so as to shorten the path of the lines of

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6. Найдите синонимические соответствия для следующих слов и словосочетаний (при необходимости воспользуйтесь словарем): to require, magnitude, to determine, certain, to undicate, quanity, entirely, path, force, while, to reduce, for example, to such an extent, i.e., utilize, owing to.

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8. Переведите предложения на русский язык, обращая внимание

2. When current flows in the solenoid, a pivoted softiron disc is attracted

towards the solenoid and the movement causes a pointer to move across a scale.

3. A moving-coil instrument, which measures only d.c., may be used in conjunction with a bridge rectifier circuit.

4. An ammeter, which measures current, has a low resistance (ideally zero) and must be connected in series with the circuit.

5. When an ammeter is required to measure currents of larger magnitude, a proportion of the current is diverted through a low-value resistance connected in parallel with the meter.

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6. Sometimes quantities to be measured have complex waveforms (, and whenever a quantity is non-sinusoidal, errors in instrument readings can occur if the instrument has been calibrated for sine waves only.

7. Such waveform errors can be largely eliminated by using electronic in-

AMMETERS AND VOLTMETERS

The action of almost all the types of measuring instruments is such that an electric current as distinct from an electric potential, is primarily responsible for the ultimate mechanical force required to produce movements of the instrument pointer. This has an exceedingly important influence on the practical forms of ammeters and voltmeters. By this is meant, that all, except the electrostatic type of instrument, are fundamentally currentmeasuring devices. They are fundamentally ammeters. Consequently, most

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voltmeters are merely ammeters so designed as to measure small values of current directly proportional to the voltages to be measured. It is only natural, therefore, that voltmeters and ammeters should be classified together.

Ammeters, which are connected in series in the circuit carrying the current to be measured, are of low electrical resistance, this being essential Сin order that they cause only a small drop of voltage in the circuit being

tested, and accordingly absorb a minimum power from it.

Voltmeters are connected across, that is, in parallel with, the circuit points where the voltage is to be measured, and are of high resistance, in this case sufficiently high so that the current flowing in the voltmeter,

и in the delicatenessбАof their construction and the restrained motion of the ro-

and the power absorbed from the circuit, are small as possible.

The principle upon which both of these devices operate is essentially the same as that of the electric motor, differing from the motor, however,

tating armature.

A coil of fine copper wire is so mounted between the two poles of a permanent magnet that its rotation is restrained by a hair spring. The farther the coil is turned from its equilibrium or zero position, the greater is the restoring force. To this coil is fastened a long pointer at the end of which is a fixed scale reading amperes if it is an ammeter or volts if it is a voltmeter. Upon increasing the current through the moving coil of an ammeter or voltmeter the resultant magnetic field between coil and magnet

in series and the voltmeter in parallel.ДThe ammeter is so connected that all the electric current passes through it. To prevent a change in the electric current when making such an insertion, all ammeters must havea low resistance. Hence, most ammeters have a low resistance wire, called a shunt, connected across the armature coil.

is distorted more and more. The resulting increase in force therefore turns the coil through a greater and greater angle, reaching a point where it is just balanced by the restoring force of hairspring.

Whenever an ammeter or voltmeter is connected to a circuit to meas-

ure electric current or potential difference, the ammeter must be connected И

A voltmeter, on the other hand, is connected across that part of the circuit for which a measurement of the potential difference is required. In order that the connection of a voltmeter to a circuit does not change the electric current in the circuit, the voltmeter must have a high resistanse. If the armature ciol does not have a large resistance on its own, additional resistance is added in series.

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Very delicate ammeters are often used for measuring very small currents too. A meter whose scale is calibrated to read thousandths of an ampere is called milliammeter, one whose scale is calibrated in millionths of an ampere being known as microammeter or galvanometer.

12.ПереработайтебАтекст, заменив формы времени Present на фор-

мы времени Past.

13.Переведите предложения наДанглийский язык.

1.Амперметры, в отличие от вольтметров, соединяются последовательно. 2. В измерительных приборах именно электрический ток обусловливает, в первую очередь, возникновение механической си-

лы. Последняя, в свою очередь, вызывает движение стрелки прибора. 3. Большинство вольтметров – это по сутиИамперметры, предназначенные для измерения малых токов, прямо пропорциональных измеряемым напряжениям. Этим объясняется то, что они обычно находятся в одном классе измерительных устройств.

14.Составьте план текстов “Electrical measuring instruments” и “Ammeters and voltmeters”. Пользуясь ответами на вопросы упражнения 9 и данными таблицы упражнения 10, подготовьте рассказ об электроизмерительных приборах.

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