Pair work. Put these questions to your groupmate and ask him/her to answer them

4 5 6 7 8 9 10

1. What is a transformer used for?

2. What does a transformer consist of?

3. What is the function of the primary winding?

4. What is the function of the secondary winding?

5. What type of transformer is called a step-up transformer?

6. What type of transformer is used for high-frequency currents?

7. What type of transformer is called a step-down transformer?

8. What type of transformer is used for low-frequency currents?

9. What is the relation between the number of turns in the windings and

the value of current?

10. What are common troubles in a transformer?

11. What should be done in case a transformer has a trouble?

Практическое занятие 10. Виды тока

Lesson 10. Types of Current

1. Read and learn the words:

Alternating - переменный

Direct - прямой

Direction - направление

Flow - течение

necessary - необходимый

to consider - рассматривать

use – использование

Read and translate the text.

Types of Current

Current is a flow of electricity through a circuit. Let us consider two main types of current: direct and alternating. A direct current (d.c.) flows through a conducting circuit in one direction only. It flows provided a direct voltage source is applied to the circuit.

An alternating current (a.c.) is a current that changes its direction of flow through a circuit. It flows provided an alternating voltage source is applied to the circuit. Alternating current flows in cycles. The number of cycles per second is called the frequency of the current. In a 60-cycle alternating current circuit the current flows in one direction 60 times and in the other direction 60 times per second.

It is easy to transform a.c. power from one voltage to another by a transformer. Transformers are also used to step down the voltage at the receiving point of the line to the low values that are necessary for use.

When necessary a.c. can be changed into d.c. but this is seldom necessary.

3. Complete the sentences using the correct variant:

1. D.c. is a current that

a) changes its direction of flow.

b) flows in one direction.

2. A.c. flows provided

a) a direct voltage source is applied.

b) an alternating voltage source is applied.

3. In an alternating current circuit

a) current flows in one direction 60 times per second.

b) current flows in one direction 60 times and in the other direction 60 times per second.

4. A.c.

a) can be changed into d.c.

b) cannot be changed into d.c.

4. 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?

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

Read about frequency, answer the question that follows. Frequency

The number of cycles per second is the frequency of an alternating current. There are two frequencies: the standard for Europe is SO cycles per second while the standard for the USA is 60 cycles per second. A standard frequency has a great advantage since different systems can be interconnected.

What is the advantage of a standard frequency?

Практическое занятие 11. Индуктивность и взаимная индуктивность

Lesson 11. Inductance and Mutual Inductance

1. Read and learn the words:

inductance - индуктивность

coil - катушка

size - размер

unit - единица

fast - быстрый

mutual - взаимный

to induce - индуктировать

to provide - обеспечить