Inductors

An inductor, also called a coil or reactor, is a passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. Energy is stored in a magnetic field in the coil as long as current flows. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, according to Faraday’s law of electromagnetic induction. According to Lenz's law the direction of induced EMF is always such that it opposes the change in current that created it. As a result, inductors always oppose a change in current.

An inductor is characterized by its inductance, the ratio of the voltage to the rate of change of current, which has units of Henries (H). Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. Along with capacitors and resistors, inductors are one of the three passive linear circuit elements that make up electric circuits. Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass; inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers.

TASK 7. Make up three sentences which would be true, false, or not given according to the information given in the text.

Model: There are only two passive linear elements in a circuit. (This sentence is false as there are three of them: capacitor, inductor and resistor)

Inductance is measured in Henries. (This sentence is true)

The coil is usually made of copper. (This information is not given; nothing is said about the material used to produce coils)

TASK 8. Listen to the recording and decide whether these statements are true or false:

1. Electricity which moves from batteries is called direct current.

2. Direct current flows from the positive electrode to the negative one.

3. Alternating current changes its polarity while it flows from positive to negative.

4. Hertz is the unit of measurement used to describe the speed of polarity change.

5. A transformer can be used to measure the current in the circuit.

6. Rectification is the process switching AC into DC with the help of diodes or transformers.

7. The ability to store electricity in an electric field is called capacitor.

8. The ability to store electricity in a magnetic field is called inductance.

9. Reactance is the way capacitors and inductors influence AC.

10. Inductance is a way to assess how easy it is for electricity to pass through an electrical device.

UNIT 9

Task 1. Study new words and word combinations.

1	adjustable resistor	[ə'ʤʌstəbl]	резистор переменного сопротивления
2	capacitance	[kə'pæsɪtənts]	емкость
3	cross-sectional area	['ɛərɪə]	площадь поперечного сечения
4	divide		делить; разделять
5	essentially	[ɪ'senʃəlɪ]	по существу
6	establish		устанавливать; учреждать
7	fixed resistor		резистор постоянного сопротивления
8	insulator	['ɪnsjəleɪtə]	изолятор
9	inductance	[ɪn'dʌktəns]	индуктивность
10	length		длина
11	measure	['meʒə]	измерять
12	oppose	[ə'pəuz]	сопротивляться, противодействовать
13	perform an experiment		проводить опыт
14	resistivity	[ˌriːzɪ'stɪvətɪ]	удельное сопротивление
15	series	['sɪəriːz]	серия, ряд
16	source	[sɔːs]	источник
17	unit		единица
18	value	['væljuː]	значение; величина
19	variable resistor	['vɛərɪəbl]	переменный резистор
20	vary	['vɛərɪ]	изменяться
21	weaken	['wiːkən]	ослаблять

TASK 2. Read the text and translate it from English into Russian.

RESISTORS

Now any circuit consists essentially of a combination of resistance, inductance and capacitance with one or more sources of electromotive force. Let us consider these main components of a circuit. At first let us speak about resistance and resistors.

The property of “opposing” or weakening the current is called electrical resistance. Georg Ohm in the early part of the 19th century performed a series of experiments which established the law connecting voltage and current. Symbolically, Ohm’s law is often written: R = V/I.

Resistance equals voltage divided by current. The unit of resistance is the Ohm. An ohmmeter is used to measure the value of resistance in a circuit. Different materials have different resistances. All substances may be divided into three groups according to their resistivities: conductors, semiconductors and dielectrics or insulators. A good conductor is a material of low resistivity. An insulator is a material of very high resistivity.

The resistance of a conductor depends on the length, the cross sectional area, the material of the conductor and its temperature. A resistor is a device employed to limit the value of current. Resistors may be fixed or variable. Fixed resistors have a constant value. The value of variable or adjustable resistors may be varied. A rheostat is another type of a variable resistor.

TASK 3. Answer the following questions and retell the text.

1. What main components does a circuit consist of? 2. What’s electrical resistance? 3. What is the unit of resistance? 4. Is an ohmmeter used to measure the value of resistance? 5. Into what groups may all substances be divided according to their resistivities? 6. What substance is called a good conductor? 7. What does the resistance of a conductor depend on? 8. Have insulators a very low or high resistance? 9. What two types of resistors do you know?

TASK 4. Read the words and pay attention to the suffixes used.

to resist – resistance – resistor; to insulate – insulator; to conduct – conductor – conduction; to depend – dependence; to discover – discovery; to produce – production; to equal – equality; to consider – consideration; to measure – measurement; to improve – improvement; to invent – inventor – invention.

TASK 5. Match the words.

1. substance a) chief

2. main b) to change

3. to use c) to regulate

4. fixed d) to produce

5. to make e) stable

6. to adjust f) material

7. to vary g) to employ

TASK 6. Fill in the gaps and translate the sentences.

1. Current passes through . . . with great difficulty. a) conductors; b) insulators; c) metals. 2. Fixed resistors have a . . . value. a) varied; b) constant; c) changeable. 3. The value of a . . . is varied. a) variable resistor; b) fixed resistor; c) very stable resistor (высокостабильное сопротивление) 4. Current equals . . . divided bу resistance. a) resistivity; b) inductance; c) voltage. 5. A . . . which is a good insulator at low temperature may be a good conductor at high temperatures. a) property; b) substance; c) source. 6. An ohmmeter is used to . . . the value of resistance in a circuit. a) divide; b) measure; c) transmit. 7. An engineer must know physical and mechanical . . . of materials. a) components; b) achievements; c) properties. 8. Mendeleyev discovered the periodic. . . . a) application; b) unit; c) law.

TASK 7. Fill in the gaps with the verbs in brackets, use the Active Voice.

1. A rheostat … (to be) a resistor whose resistance value may be varied. 2. Last week they … (to make) many experiments. 3. Any circuit … (to consist of) a combination of resistance, inductance and capacitance. 4. Next week he … (to demonstrate) this new device. 5. Popov … (to invent) the first radio-set. 6. A resistor … (to be) a device to limit the value of current. 7. An ohmmeter … (to measure) the value of resistance in a circuit. 8. Resistance … (to equal) voltage divided by current.

TASK 8. Fill in the gaps with the verbs in brackets, use Participle II.

1. The work … (to do) by these scientists resulted in many new discoveries. 2. A new transmitting station … (to build) in our region is very powerful. 3. The phenomenon … (to study) by this engineer is of great importance for our work. 4. Radio waves … (to radiate) by the antenna travel in all directions. 5. The experiments … (to make) by him were very useful for our work. 6. New measuring instruments … (to develop) in this laboratory will be used in this experiment. 7. A device … (to employ) to limit the value of current is a resistor. 8. The antenna receives only a small part of energy … (to radiate) by the transmitter.

TASK 9. Listen to the recording and fill in the gaps.

Apprentice Tech: Could you explain how to replace a 1) …?

Senior Tech: Sure. It's not that hard to do. The first thing is 2) … to find which resistor or resistors are bad.

Apprentice Tech: Okay. I already did that.

Senior Tech: So did you 3) … any bad resistors?

Apprentice Tech: Yes. I found one. But I haven’t 5) … it yet.

Senior Tech: Good. Are the 6) … still visible?

Apprentice Tech: Yes.

Senior Tech: Then, what you need to do is 7) … its value based on 8) … of the bands. After that you remove it.

Apprentice Tech: I cut the 9) … leads. Right?

Senior Tech: Yes, but the tricky part is that you don’t you need to touch any of the 10) …, so be sure to use diagonal cutters.

Apprentice Tech: I see.

Senior Tech: Then finish up by soldering in a new resistor with the same 11) … as the original.

Apprentice Tech: Thanks.