2020-04-07
2236
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 o f 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 varying 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 in this coil though the two coils do not touch. The secondary voltage, that is the voltage in coil B, is called induced voltage and energy from one coil to the other transfers by induction. The coil across which the current is applied is called the primary, that in which voltage is induced is called the secondary. The primary and the secondary coils have
mutual inductance. Mutual inductance is measured in the same units as inductance, that is in henries.
Thus, when a rate of change of one ampere per second in the primary coil will produce one volt in the secondary coil, the two coils have one henry of mutual inductance. It should be taken into consideration that induction by a varying current results from the change in curren t not in the current value. The faster the current changes, the higher the induced voltage.
3. Complete the sentences using the correct variant:
1. Any conductor has
a) some definite value of resistance,
b) some definite value of inductance.
5. Any conductor can provide
a) electric power.
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b) induced voltage.
6. Elements with a definite value of inductance
a) are called inductors.
b) are called coils.
c) are called sources.
7. The inductance of a coil depends upon
a) its size.
b) its core.
c) its material.
d) its number of turns.
8. An iron core
a) increases the value of inductance.
b) decreases the value of inductance.
6. The value of mutual inductance is measured
a) in watts.
b) in henries.
7. Induction by a varying current
a) results from the change in current.
b) results from the change in the current value.
8. The faster the current changes,
a) the lower is the induced voltage.
b) the higher is the induced voltage.
4. Answer the following questions:
1. What value of inductance do conductors have?
2. What is the function of inductors?
3. What are elements with a definite value of inductance called?
4. What does the inductance of a coil depend upon?
5. How does the inductance of a coil depend upon the material of its core?
6. In what units is the value of mutual inductance measured?
7. What does induction by a varying current result from?
8. What is the relation between the current changes and the value of induced
voltage?
9. What is the unit of resistance?
10. What is the unit of potential difference?
11. For what type of current is an air core used?
12. What is the relation between the number of turns of a coil and its inductance
value?
Pair work. Tell your groupmate about mutual inductance.
Практическое занятие 12. Взаимосвязь
Lesson 12. Coupling
1. Read and learn the words:
Device - прибор
field - поле
loose - свободный, нежесткий
tight - плотный
self-inductance - самоиндукция
to couple - соединять, сцеплять
to separate - отделять
to transfer - переносить
therefore - поэтому
Read and translate the text.
Coupling
When circuits are indirect-inductively coupled energy is transferred from one circuit to another using electromagnetic field of the inductance through which a varying current is flowing.
The coupling device is a transformer. It is not in series with the elements of the circuit, therefore the coupling is indirect. The transformer consists of two windings: the primary and the secondary. The primary circuit is connected to the voltage source, the secondary - to the load circuit. The coupling may be tight and loose. In case the coils of the coupling element are close together, the coupling is tight.
In case the coils are separated the coupling is loose. In the loose coupling the mutual inductance is small compared with the self-inductance.
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3. Complete the sentences using the correct variant:
1. The circuit connected to the voltage source is called
a) the secondary circuit.
b) the primary circuit.
2. The circuit receiving its energy through a coupling is
a) the primary circuit.
b) the secondary circuit.
3. The function of a coupling element is
a) to separate the circuits.
b) to transfer energy.
c) to prevent a short between the circuits.
4. When the coupling is tight
a) the coils are separated.
b) the coils are close together.
5. When the coils are close together
a) the coupling is loose.
b) the coupling is tight.
6. The circuits are indirectly coupled when
a) the coupling element is common to both circuits and is in series with their
other elements.
b) the coupling element is not common to the circuits and is not in series with
their other elements.
4. Complete these sentences using while.
1. The circuit receiving energy is the secondary circuit....
2. The coupling is loose when the coils are separated..........
3. When the coupling element is not common to the circuits and not in series
with their elements, the circuits are indirectly coupled..........
5. Answer the following questions:
1. What type of circuit is called the primary?
2. What type of circuit is called the secondary?
3. What is the function of a coupling element?
4. What type of coupling is called loose?
5. What type of coupling is called tight?
6. In what case are the circuits directly coupled?
7. In what case are the circuits indirectly coupled?
8. What is the difference between a tight and loose coupling?
9. In what case should a coupling element be substituted?
Pair work.
Draw a scheme of 1) a loose coupling, 2) a tight coupling.
Describe the schemes to your groupmate.
