II. Выберите из правого столбика нужные словосочетания, чтобы закончить предложения.

     

1. Assume that armature loop is rotating...	... through fewer and fewer lines of force.
2. At nought degrees the black and white conductors of the loop are moving...	... through a maximum number of lines of force.
3. At 90 degrees conductors are cutting...	... parallel to a magnetic field.
4. As the loop is rotating from 90 degrees to 180 degrees the conductors begin to cut...	... in a clockwise direction.

 

III. Напишите первые три предложения из упражнения II в прошедшем и будущем времени.

 

Образец: they are moving parallel to a magnetic field;

they were moving ...;

they will be moving ... .

 

IV. Ответьте на вопросы, употребив слова yes, no.

 

1. Is any e.m.f. induced at nought degrees?

2. Does the induced e.m.f. build up between 0 to 90 degrees?

3. Does the induced e.m.f. decrease as the loop moves from 90 to 180 degrees?

4. Is the e.m.f. generated in the conductor if it is moving parallel to a magnetic field?    

5. Does the direction of the cutting action of conductors through the magnetic field reverse as the loop starts rotating beyond 180 degrees back to position A (nought degrees)?

 

V. Просмотрите текст и расскажите, употребив данные слова и словосочетания, о том, что происходит:

1) когда проводник движется параллельно магнитному полю: conductor, clockwise direction, the armature loop, magnetic field, at nought degrees, lines of force, no e.m.f., assume, is rotating, is moving parallel to, doesn’t cut through, is generated;

2) когда петля вращается от 0° до 90°: loop, position, conductors, more and more lines of force, induced e.m.f., maximum number of, maximum value, rotates (from ... to), are cutting through, builds up to;  

3) когда петля вращается от 90° до 180°: (fewer and fewer) lines of force, no longer, the induced e.m.f., continues, cut through, decreases;

4) когда петля вращается за 180°: beyond, direction of cutting action, as a result, polarity, current flow, rotates, reverses, will reverse.

 

 

Text 3

The Commutator

 

In the elementary generator the a.c. voltage induced in the loop reverses its polarity every time the loop goes through the 0 degrees and 180 degrees points. At these points the conductors of the loop reverse their direction through the magnetic field. As you already know, the polarity of the induced e.m.f.  depends on the direction a conductor moves through a magnetic field; and if the direction reverses, the polarity of the induced e.m.f. reverses. Since the loop continues rotating through the field, the conductors of the loop will always have an alternating e.m.f. induced in them. Therefore the only way thatd.c.can be obtained from the generator is to convert the generated a.c. to d.c.

One way to do this is to have switch connected across the generator output in such a way that it will reverse the connections to the load every time the polarity of the induced e.m.f. changes inside the generator.

In order to convert the generated a.c. voltage into a varying d.c. voltage the switch must be operated twice for every cycle. If the generator output is alternating at 50 cycles per second, the switch must be operated 100 times per second to convert the a.c. to d.c. It would be impossible to operate a switch manually at such high speed.

A solution has been found in the rings of the elementary generator. One of the slip rings is eliminated, and the other is split along its axis. The ends of the coil are then connected one to each of the segments of the slip ring. The segments are insulated so that there is no electrical contact between segments, the shaft or any other part of the armature. The entire slip ring is known as the "commutator", and its action of converting a.c. to d.c. is known as "commutation".

The brushes are now positioned opposite each other, and the commutator segments are mounted so that they are short-circuited by the brushes as the loop passes through novoltage points. As the loop rotates each conductor will be connected by means of the commutator, first to the positive brush and then to the negative one.

When the armature loop is rotated, the commutator automatically switches each end of the loop from one brush to the other every time the loop completes a half revolution. The action is exactly the same as that of the reversing switch.

Words and Word Combinations

commutator n	коммутатор, коллектор
alternating a	меняющийся, переменный, колеблющийся
the only way	единственный способ
obtain v	получать
have a switch connected	соединить выключатель
connection n	соединение
switch 1. v       2. n	переключать переключатель
output n	мощность (отдаваемая)
impossible a	невозможный
to operate manually	управлять вручную
solution n	решение
find (found, found) v	находить
eliminate v	удалять
split v	расщеплять
along its axis	по его оси
coil n	катушка
insulate v	изолировать
shaft n	вал
entire a	весь, все
to be known v	быть известным
commutation n	коммутация (перемена направления тока)
brush n	щетка
position v	размещать
mount v	монтировать, устанавливать
short-circuit v	закорачивать, замыкать накоротко
pass v	проходить
complete v	заканчивать
exactly adv	точно
reversing switch	реверсивный переключатель

 

Notes: depends on the direction a conductor (moves through a magnetic field) – зависит от направления, в котором проводник ...

(the action) is the same as that of ... – ... такое же как действие ...

 

E x e r c i s e s

I. Прочитайте и переведите следующие слова:

 

polarity, commutator, commutation, axis, alternating e.m.f., impossible, revolution, solution, to position – are positioned, to convert – converting, to mount – are mounted, automatically, manually, exactly, depends, changes, switches (switch).

 

II. Найдите в тексте эквиваленты следующих слов и словосочетаний:

в этих точках, продолжает вращаться, чтобы превратить, с каждым из сегментов, проходит через точки без напряжения.

 

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