Perfect Tenses (Active, Passive)

Времена (Present, Past, Future) группы Perfect обра­зуются при помощи вспомогательного глагола to have в соответствующем времени, лице и числе и причастия прошедшего времени смыслового глагола (Participle II).

Формула образования Perfect Tenses

to have Participle II

в соответствующем + смыслового глагола

времени, лице и числе

Например:

Не has spent some years on his experiments, so the results obtained may be trusted. — Он потратил несколько лет на эксперименты, и поэтому можно доверять полученным им результа­там.

Не wrote about all he had seen during those five long years. — Он написал обо всем, что он видел в эти долгие пять лет.

The technician will have recorded the data before you come. — Техник зарегистрирует все данные до вашего прихода.

Сравнительно часто в технической литературе упо­требляется Present Perfect Passive, который образуется по формуле образования страдательного залога

to be + Participle II,

причем to be берется соответственно в нужном перфектном времени

have been

had been Participle II

will have been

Например: The device has been repaired. — Прибор исправлен.

УПРАЖНЕНИЕ

1. Поставьте глагол, стоящий в скобках, в соответствующее время и залог группы Perfect:

1. In a series of experiments carried out during ten days in the autumn of 1831, Faraday established the foundation upon which our electrical age (to build). In 1816 Davy wrote: "I (to make) very simple and economic lanterns, which may be useful to the miner." The problem how electricity could be produced (to face) the scientist Volta, and the device with which he solved it is named after him.

Прочтите и переведите текст:

TEXT

THE CAPACITOR

A capacitor is an electrical device for storing quantities of electricity in much the same way that a reservoir is a container for storing water or a steel tank is a container for storing gas. The general form of a capacitor is that of two parallel conducting plates as shown in Fig. 12.

Such plates are of relatively large area, close together, and contain between them a nonconducting medium called the dielectric. Common dielectrics are air, glass, oil and waxed paper.

Quantitatively, the capacitance of a capacitor is a measure of its ability to store-up electricity. To increase the capacitance of a capacitor, one of the following changes can be made: first, the area of the plates may be increased; second, the plates may be put closer together; and third, a more suitable dielectric may be inserted between the plates. If the plates of a capacitor are small in area and at the same time relatively far apart, the capacitance is small. If the area is large and the plates close together, the capacitance is large.

The principles of the capacitor are illustrated in Fig. 12. One plate of this capacitor is grounded, and the other is insulated but connected to an electroscope or electrometer. If the right-hand plate is now given a negative charge as shown, electrons in the other plate are repelled into the ground, leaving that plate positively charged. If the insulat­ed plate is given a positive charge (not shown), electrons from the ground are attracted to the other plate and it's acquired a negative charge.

In either case the grounded plate is, by definition, at ground potential or zero potential. The right-hand plate is at negative potential, since, if connected to the ground, its electrons would escape into the ground. As shown in the diagram, the capacitor is charged. If the two plates of a capacitor are suddenly connected by a conductor the negative charges can flow through the conductor to the positive charges, thus neutralizing the charges. The capacitor has thus been discharged.

During the time a capacitor is being charged, the plates acquire a greater and greater difference of potential. If in Fig. 12 more electrons are added to the insulated plate, the potential difference is increased. The amount of charge stored-up in this way is limited only by the breakdown of the dielectric between the two plates. When the charge becomes too great, a spark will jump between the plates, thus discharging the capacitor.

The unit of capacitance, the farad, named in honour of Michael Faraday, is defined as the capacitance of a capacitor of such dimensions that a charge of one coulomb will give the plates a difference of potential of one volt:

1 farad = 1 coulomb / 1volt

A capacitance of 1 farad is very large and for practical purposes is not used. The microfarad is more convenient. The smaller unit is one-millionth of the farad and is abbreviated mf. In other words, 1,000,000 microfarads are equivalent to 1 farad. A still smaller unit, the micro-microfarad, is sometimes used. One micromicrofarad is one-millionth of 1 microfarad and is abbreviated mmf.

Capacitors in common use today are of various kinds, sizes and shapes. Perhaps the most common is the so-called "paper capacitor" used commonly in radios and the ignition system of automobiles. Another type of capacitor is the variable capacitor commonly used in tuning radios. The capacitance of such a device can be varied by the turning of a knob. The capacitance of such variable air capacitors is from zero to about 4000 mmf.

УПРАЖНЕНИЯ

I. Используя таблицы на стр. 8 — 13, образуйте слова
однокоренные с данными:

quantity — количественный, — количественно

to contain — контейнер

to conduct — проводник, — проводящий, — непро­водящий

to measure — измерения, — поддающийся измере­ниям

relative — относительно

increase — уменьшать

limit — лимитированный

to differ — различие, — отличающийся

common — обычно

to vary — различные, — изменения

II.Определите функцию выделенных слов:

1. A capacitor is used for storingelectricity. 2. Two parallel conductingplates are shown in the diagram. 3. A nonconductingmedium is called the dielectric. 4. If the right-hand plate is now given a negative charge, electrons in the other plate are repelled into the ground leavingthat plate positively charged.5. In either case the groundedplate is at groundpotential. 6. If the insulatedplate is given a positive charge,electrons from the groundare attracted to the other plate. 7. When the chargebecomes too great, a spark will jump between the plates thus dischargingthe capacitor.

III.Ответьте на вопросы:

1. What is the difference between a capacitor and capacitance? 2. How can the capacitance of a capacitor be increased? 3. What is the principle of the capacitor? 4. How is the capacitor discharged? 5. What unit is used for measuring capacitance? 6. What unit is used for practical purposes? 7. What types of capacitors are the most common?

Задание 12