III. Find English equivalents.

Сердечник, виток, обмотка, повышать, понижать, частота, из-за.

IV. Finish the sentences.

1. A transformer is used………

2. A two-winding transformer………

3. The value of voltage…….

4. In case the secondary has……………

5. The voltage in the secondary i_{s……………..}

6. Common troubles in transformers are…………

7. Current transformers are used……………….

8. Current transformers also insulate…………..

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

1.The secondary winding of a transformer is connected to the load re­sistance ....

2. The primary winding receives energy....

3. A step-down transformer decreases the primary voltage....

4. An air core transformer is used for high-frequency currents

5. In a step-up transformer the number of turns of the secondary winding

is greater than the number of the primary winding……..

VI. Read about current transformers. Answer the questions that follow. Current Transformers

Current transformers are used for operating ammeters, wattcmeters, ant other measuring devices. They produce in the meters a current lower that the measured current but proportional to it.

Current transformers also insulate the instrument from the circuit which is being measured. This is necessary for high voltage circuits.

1. What is a current transformer used for?

2. What type of current does it produce?

VII. Answer the questions.

What is a transformer used for?

What does a transformer consist of?

What is the function of the primary winding?

What is the function of the secondary winding?

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

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

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

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

What is the relation between the numbers of turns in the windings is the value of current?

What are common troubles in a transformer?

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

Практическая работа № 11 types of current

Цели: Введение и активизация в речи лексики по теме «Виды электрического тока».

Оборудование: комплект тестов, раздаточный материал.

Vocabulary

I. Learn the words and expressions.

Alternating переменный

Direct прямой

Direction направление

Flow течение

Necessary необходимый

To consider рассматривать

Use использование

II. Read and translate the text.

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.

III. Find English equivalents.

Необходимый, течение, прямой, рассматривать, использование, переменный

IV. Add necessary letters.

Dire-tion, pro­v-ded, alte-nat-ng, ele-tri-ity, c-cles, fre-ue-cy, re-eiv-ng, ne-­es-ary.

V. Finish the sentences.

1. A direct current flows ………

2. An alternating current is………

3. The number of cycles……….

4. Transformers are also used to…………

5. When necessary alternating current can………

VI. Make up the sentences.

1. electricity is a a circuit flow of Current through

2. A conducting circuit current flows one a in direction direct through only.

3. of cycles is called per the current second The number of the frequency.

4. It is a.c. to another power easy to transform transformer voltage from one by a

5. a.c. into D.C can be changed but this. seldom is When necessary nec­essary.