Контрольная работа №2

(2 курс Рз, Рзс (2семестр))

ВАРИАНТ 1

3адание.1. Сделайте письменный перевод текста.

In recent years the transistor — an entirely new type of electron device - replaces the bulky electron tubes in many applications. Transistors are far smaller than tubes, have no filament and hence need no heating power. They are mechanically rugged, have practically unlimited life, and can do some jobs better than electro tubes. In contrast to electron tubes, which utilize the flow of free electrons through a vacuum or gas, the operation of transistors is based on the movement of charge carriers through a solid substance, a semiconductor. Transistors are only one of the family of Semiconductors; many other semiconductors applications are becoming increasingly popular and new ones are constantly being discovered.

It is known that materials are classed as semiconductors if their electrical conductivity is intermediate between metallic conductors, which have a large number of free electrons available as charge carriers, and non—metallic insulators, which have practically no free electrons available to conduct current. The two semi provided with a small diameter filament).

This third electrode is an open wire structure through which electrons can pass (of the order of a few percent) and is called the control grid. It often takes the form of a fine wire helix. Electrons can pass through the control grid unimpeded, but the electric field at the cathode surface can be changed by varying the electric potential of the control grid. There are two important features of such a grid that enable the triad. valves to be used as voltage amplifiers. If the grid is placed physically very close to the cathode small changes of the voltage between the cathode and grid will produce a large. change of electric field in the cathode — grid region and therefore a large change of current through the valve. Moreover the grid has a potential which is slightly negative relative to the cathode no electrons can travel from the cathode to the grid and hence no conduction current flows in the grid circuit. If no current is taken from the grid supply no power is required to change the grid voltage and to change the grid current. This is why very small signals from a radio antenna can produce significantly great effect in the first stage of a radio receiver.

3адание 2. Внимательно просмотрите текст. Найдите и выпишите глаголы в страдательном залоге. Переведите эти словоформы.

Задание 3. Ответьте на следующие вопросы:

1. What is the difference in operation between electron tubes and transistors?

2. What are the advantages of transistor application?

3. What is the peculiarity of non—metallic insulators?

4. What is termed a covalent bond?

Задание 4. Составьте сообщения по предложенным ситуациям

I. Your ship's propeller is caught with wire ropes. You're drifting to the sunken rock ahead of you. The sea is rough. You require immediate assistance.

2. As a result of the collision with another ship you have received a large gash in the bottom tank. The sea is coming into it.

3. Your ship ran aground in position... You have got a hole. You cannot refloat without tug assistance. You try to patch the gash yourselves. But at the same time you ask for help to tow you off the ground.

4. Your ship is burning. Your crew members are abandoning the ship in life boats. You ask to render you immediate assistance. What way would you act?

КОНТРОЛЬНАЯ РАБОТА №2

(2 курс Рз, Рзс (2семестр))

ВАРИАНТ 2

3адание.1. Сделайте письменный перевод текста.

Vacuum tubes are able to convert alternating currents- to-direct currents. This is known as rectification”. Rectification is an inherent property o vacuum tubes because current can flow only in one direction from a source of electrons. If a sinusoidal wave of voltage is applied to a vacuum tube of the right type, current will flow in only one direction, causing a series of half—wave pulses all of the same polarity. It is possible to connect another like tube to insert half—wave pulses of the sane polarity between the pulses of the first tube. The average of these pulses constitutes a direct current; the other frequency components are rejected by a filter circuit

Rectification is important because electronic devices operate best on direct current, while power is usually generated and transmitted in alternating form. It is thus necessary to convert or rectify the a.c. power into d.c. power,

When a third electrode is inserted between the filament and the plate, the vacuum tube is enabled to perform other operations. This electrode is called the control grid and is generally in the shape of laterally wound wire or mesh whose turns are spaced so as to permit a current flow from filament to the plate, It is also insulated from other electrodes, its purpose is to control the flow of plate current.

The quantity of electrons attracted to the plate depends upon the combined effect of the plate and grid charges. When the plate is positive normally, and the grid voltage is made more and more negative, the plate is less able to attract electrons and the plate current decreases.

Задание 3. Ответьте на следующие вопросы:

1. Why is rеctification important?

2. In what case will current flow in only one direction?

3. What is called a control grid?

4. What does a quantity of electrons attracted to the plate depend on?

Задание 4. Составьте сообщения по предложенным ситуациям:

1. You have discovered a capsized yacht in position…You are searching for men

overboard. You ask immediate assistance.

2. Your vessel is involved in collision with unknown ship in thick fog. Your vessel

is slowly sinking.

3. You are not under command in position. The sea is calm. You need a tug to tow

you to the nearest port.