II. Read and translate the text.

 

This filter is used to separate direct cur­rent from alternating current. It consists of a capacitor and a choke coil. Direct current cannot flow through the capacitor since its R, D.C-* insulators oppose the flow of direct cur­rent. Therefore, it flows through the choke coil. Its windings easily pass direct current through them. Alternating current, on the other hand, passes through the capacitor, since it cannot easily pass through the choke coil. In this way the direct and the alternating currents are separated.

I. A high-pass filter is used to pass high frequencies and to prevent the flow of low frequencies. It consists of a condenser and an inductance coil. The condenser passes currents of high frequencies and opposes the flow of low frequency currents. Low frequencies must be returned to the source and the inductance coil is used for a bypass.

II. A low-pass filter is used to pass low frequencies and to prevent the flow of high frequencies. It consists of an inductance coil and a con­denser. The inductance coil passes low frequencies and opposes the flow of high frequencies. To return the high frequencies back to the source, a condenser is used for a bypass. Its capacity opposes the flow of low fre­quencies through it.

 

   III. Finish the sentences

1. This filter is used…….

2. A high-pass filter is used………….

3. A low-pass filter is used…………

4. Choke input filter is…………

5. Capacity input filter is……………..

IV. Complete these sentences using on the other hand. Follow the model.

 

Model: Direct current passes through the choke coil of a filter; alternating current, on the other hand, passes through the capacitor.

1.A low-pass filter is used to pass low frequencies       

2.In a high-pass filter an inductance coil is used as a bypass....

3.A high-pass filter is used to prevent the flow of low frequencies     

4.Alternating current passes through a capacitor

V. Draw schemes of a choke input filter and a capacity input filter. De­scribe the schemes and the function of the filters.

 

VI. Read the text and answer the question that follows it.

               Rectify     выпрямить

               Eliminate     устранить

A choke input filter and a capacity input filter are used in rectifiers Filters of this kind are connected to rectifiers in order to eliminate pulsations produced in rectified current.

1)Choke input filter is a low-pass filter. A choke coil is in series with the rectifier output.

2) Capacity input filter is a high-pass filter. A capacitor is connected directly across or in parallel with the rectifier output.

  VII. What is the difference between a choke input filter and a capacity in­put filter?

 

VIII.  Answer the following questions:

1. What is a filter used for?

2. What does a filter consist of?

3. What is the function of a low-pass filter?

4. What is the function of a high-pass filter?

5. What is the difference between a low-pass filter and a high-pass filter?

6.What elements are used as a bypass?

7. What is the function of a choke coil?

 

                                  ПРАКТИЧЕСКАЯ РАБОТА № 13

                                                     

ELECTRON TUBES

 

Цели: Введение и активизация в речи лексики по теме «Электронные лампы».

Оборудование: комплект тестов, раздаточный материал.

 

 

                             Vocabulary

I. Learn the words and expressions.

 

Tube                                                    электронная лампа

Bulb                                                         баллон

Grid                                                         сетка

Screen                                                       экран

To contain                                            вмещать

To collect                                             собирать

To emit                                                 излучать

To suppress                                          глушить, подавлять

Control circuit                                       контрольная цепь

Control grid                                         управляющая сетка

Screen grid                                          экранирующая сетка

Screen grid tube                                   экранированная лампа

Suppressor grid                                     защитная сетка

Counter flow                                        противоток

Oscillatory circuit                                 колебательный контур

 

 II. Read and translate the text.

 

Let us consider electron tubes. Among the electron tubes in use nowadays there are a diode, a triode, a tetrode and a pentode. The main parts of electron tubes are electrodes. Electrodes are placed into a glass or metal bulb.

A diode contains the cathode and the plate. When a diode operates the cathode emits electrons, the plate collects them.

A triode contains the cathode, the plate and the control grid. When the tube operates the cathode emits electrons, the plate collects them

and the grid controls the flow of electrons. Therefore, the grid is called a control grid.

A tetrode contains the cathode, the plate, the control grid and the screen grid.

When a tube operates it may oscillate. The function of the screen grid is to eliminate oscillations. Therefore it is called a screen grid.

A pentode contains two electrodes and three grids: the control grid, the screen grid and the suppressor grid. When a pentode operates the suppressor grid eliminates the secondary emission.

Common troubles in tubes are an open heater and low emission.

These troubles result from constant use or from some other reason. In case a tube has a trouble it stops operating or operates badly. A tube with a trouble should be replaced by another one.