VII. Complete these sentences using while. Follow the model on page 13.

1. An alternating current changes its direction of flow

2. A direct current flows provided a direct voltage source is applied ...

VIII. Answer the following questions:

1. What is current?

2. What types of current do you know?

3. When does a direct current flow?

4. What type of current is called an alternating current?

5. What type of current is called a direct current?

6. What is called the frequency of current?

7. What device is used to transform a.c. power from one voltage to another?

8. Is it often necessary to change a.c. into d.c?

Практическая работа № 12 filters

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

Оборудование: комплект тестов, раздаточный материал.

Vocabulary

I. Learn the words and expressions.

Filter фильтр

Bypass шунт

Choke дроссель

High-pass высокопроходной

Low-pass низкопроходной

To oppose оказывать сопротивление

On the other hand с другой стороны

Choke coil дроссельная катушка

Bypass co шунтовая катушка

Bypass condenser шунтирующий конденсатор

High-pass filter фильтр верхних частот

Low-pass filter фильтр низких частот

Opposing coils противодействующие витки

Opposed current противоток

II. Read and translate the text.

T his 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.

1. 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.

2. 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