Inductance and Mutual Inductance

Any conductor has some definite value of inductance. The induc­tance of a conductor shows how well it can provide induced voltage.

Elements of a circuit with a definite value of inductance are coils of wire called inductors. The inductance of a coil depends upon its size and material. The greater the number of turns of a coil, the higher is its inductance. An iron core also increases the value of inductance. Coils of this type are used for low-frequency currents while coils with an air ^core are used for high-frequency currents.

Two coils A and В are brought close together and a source of vary-^lng current is applied to coil A. If a measuring device is connected across the terminals of coil В it will be found that a voltage is induced ^ln this coil though the two coils do not touch. The secondary voltage, ^tnat is the voltage in coil B, is called induced voltage and energy from °ne coil to the other transfers by induction. The coil across which the

-31-

*

current is applied is called the pri\ тагу; that in which voltage is in* duced is called the secondary. The primary and the secondary coils have mutual inductance.Mutual indue tance is measured in the same unitsas inductance, that is in henries. Thus, when a rate of change o| one ampere per second in the primarj coil will produce one volt in the sec ondary coil, the two coils have onej henry of mutual inductance. It should be taken into consideration that induction by a varying cur rent results from the change in currentnot in the current value.Th^ faster the current changes, the higher the induced voltage. 4. Complete the sentences using the correct variant:

£^МЛ

Fig. 12

1. Any conductor has

2. Any conductor can provide

3. Elements with a definite value of inductance

4. The inductance of a coil de­pends upon

5. An iron core

6. The value of mutual induc­tance is measured

7. Induction by a varying current

8. The faster the current changes, a

some definite value of resistance, some definite value of inductance.

electric power, induced voltage.

are called inductors, are called coils, are called sources.

its size.

its core.

its material.

its number of turns.

increases the value of inductance, decreases the value of inductance.

in watts, in henries.

results from the change in current results from the change in the cur­rent value.

the lower is the induced voltage, the higher is the induced voltage.

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

1. An air core decreases the value of inductance.............

2. An iron core is used for low-frequency currents..............

3. The coil in which voltage is induced is called the secondary.............

6. Answer the following questions:

What value of inductance do conductors have? What is the function of inductors?

What are elements with a definite value of inductance called? What does the inductance of a coil depend upon? How does the inductance of a coil depend upon the material of its core?

In what units is the value of mutual inductance measured? What does induction by a varying current result from? What is the relation between the current changes and the value of in­duced voltage?

9 10 11 12

What is the unit of resistance? What is the unit of potential difference? For what type of current is an air core used?

What is the relation between the number of turns of a coil and its in­ductance value?

7. Pair work. Tell your groupmate about mutual inductance. Let him/her put the questions of Exercise 6 to you and answer them.

a) Cover the right column and read the English words. Translate them into Russian and check your translation.

b) Cover the left column and translate the Russian words back into English.

device	[diVais]	прибор
field	[fi:ld]	поле
loose	[to*]	свободный, нежесткий
tight	[tait]	плотный
self-inductance		самоиндукция
to couple	1'клр1]	соединять, сцеплять
to separate	['separeit]	отделять
to transfer	[traens'Ia:]	переносить
therefore	I'deafo:]	поэтому

-38

-39-

Дата добавления: 2015-05-08