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b) common insulators

four. air, newspaper and plastics are

a) mutual insulators

b) common conductors

five. in case a high voltage is practical to an insulator

a) information technology does not acquit electric current

b) information technology conducts current

half dozen. insulators are used

a) to store electrical charge

b) t) reduce voltage

c) to foreclose a short between conducting wires

7. metals increment their resistance

a) when the temperature decreases

b) when the temperature increases

8. carbon decreases its resistance

a) when the temperature increases

b) when the temperature decreases

9. metals have

a) a positive temperature coefficient fifty of resistance

b) a negative temperature coefficient fifty of resistance

Cease the sentences using the words with the opposite meaning:

1. Conductors accept a low resistance � � . ii. Current passes through insulators with great difficulty... ... .

three. Metals are mutual conductors... ... . four. To make insulators comport, currents of smashing value must be applied... ... . five. Carbon decreases its resistance when the temperature increases... . half dozen. Metals have a positive temperature coefficient of resistance....

Answer the following questions:

What is the divergence between conductors and insulators? 2. How does current pass through insulators? 3. What materials are commonly used to produce insulators? 4. What materials are commonly used to produce conductors? 5. In what case do insulators conduct current? vi. How does resistance change when the temperature decreases?

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1 - b; 2 - a; 3 - a; 4 - a; 5 - b; six - a, c; 7 - b; 8 - a; 9 - a.

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1. Insulators ��... high

2. conductors ��.. hands

3. air, paper, rubber, plastics �� insulators

four. conductors ��.. low

5. metals ��. Increase

half dozen. carbon ��. negative

1. a value of resistance

ii. with great difficulty

3. air, paper, prophylactic, plastics

four. metals

five. a loftier voltage is practical

6. carbon increases, metals decrease.

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Lesson 9
TRANSFORMERS
transformer	number
transfer	turn
core	receive
winding	stride up
primary winding	frequency
secondary winding

A transformer is used to transfer energy; due to the transformer electric power may be transferred at a high voltage and reduced at the point where it must exist used to any value. Besides, a transformer is used to modify the voltage and electric current value in a circuit.

A two-winding transformer consists of a closed core and two coils (windings). The primary winding is connected to the voltage source. Information technology receives free energy. The secondary winding is continued to the load resistance and supplies energy to the load.

The value of voltage across the secondary last de�pends on the number of turns in it. In case it is equal to the number of turns in the primary winding the voltage in the secondary winding is the same as in the main,

In instance the secondary has more turns than the chief the output voltage is greater than the input voltage. The voltage in the secondary is greater than the voltage in the main by every bit many times as the number of turns in the secondary is greater than the number of turns in the pri�mary. A transformer of this type increases or steps up the voltage and is chosen a footstep up transformer. In case the sec�ondary has fewer turns than the primary the output volt�age is lower than the ch a transformer decreases or steps downwardly the voltage, it is called a stride down transform�er.

Compare T1 and T2. T1 has an iron core. For this reason it is used for low frequency currents. T2 has an air core and is used for high frequencies.

Common troubles in transformers are an open in the winding, a brusque between the primary and the secondary, and a short between turns. In instance a transformer has a trouble it stops operating or operates desperately. A transformer with a trouble should be substituted.

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EXERCISES

Find the right variant. Recall information technology:

one. a transformer is used

a) to shop charge

b) to preclude the alter of energy

c) to transfer energy

d) to modify the voltage and current value in a circuit

2. electric power is transferred at a high voltage and reduced

to any value

a) due to resistors

b) due to capacitors

c) due to transformers

3. a transformer consists of

a) cores but

b) the primary and the secondary windings

c) a core and the principal and the secondary windings

4. the office of the primary is

a) to prevent the change of voltage

b) to supply energy

c) to receive energy

d) to transfer charge

5. the function of the secondary is

a) to receive energy

b) to supply free energy

c) to transfer energy

d) to decrease the value, of charge

six. a step up transformer is used:

a) to stride down or decrease the secondary voltage

b) to step up or increase the main voltage

7. a step down transformer is used

a) to step downwardly the secondary voltage

b) to step down the main voltage.

8. a transformer with an atomic number 26 core

a) is used for high frequency currents

b) is used for depression frequency electric current:,

nine. a transformer with an air core is used

a) for high frequency currents and for depression frequency currents

b) for high frequency currents only

x. in a step upwardly transformer

a) the number of turns of the secondary winding is greater than the number of turns of the

primary

b) the number of turns of the primary winding is greater than the number of turns of the secondary

Two. a transformer should exist substituted

a) in case information technology has an open in the winding

b) in case it has a short between the chief and the

secondary

c) in case information technology has a brusk betwixt turns

End the sentences using the words with the opposite significant:

i. 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 chief voltage.... 4. An air core transformer is used for high frequency currents. .. .... 5. In a footstep upwardly transformer the number of turns of the secondary winding is greater than the number of turns of the primary winding... ..... ..

Answer the following questions:

1. What is a transformer used for? 2. What does a transformer consist of? three. What is the office of the primary winding? 4. What is the function of the secondary winding? 5. What type of transformer is called a stride up transformer? six. What type of transformer is used for high frequency currents? 7. What blazon of transformer is chosen a footstep downwardly transformer? 8. What type of transformer is used for low frequency currents? nine. What is the relation between the number of turns in the windings and the value of current? x. What are common troubles in a transformer? 11. What should be done in instance a transformer has a trouble

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1-�, d,. ii-�, three-�, 4-c, 5-b, half dozen-b, seven-b, 8-b, 9-b, x-a, xi-a, b,c.

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1. The primary winding... voltage source

ii. pplies

3. a pace upwardly,.. increases

4. atomic number 26...low

5. pace down... primary... secondary

ane. to transfer free energy, to change the voltage and current value

2. a closed core and two coils

three. it receives energy

4. it supplies free energy

v. information technology steps upwards the voltage

6. an air cadre

seven. it steps down the voltage

eight. an iron cadre

9. the greater... the greater

ten. an open in the winding, a brusk between windings, a short between turns

11. should be substituted.

Lesson 10
TYPES OF CURRENT
flow	alternating
direct	cycle
direction	'per 'second

Current is a catamenia of electricity through a circuit. Let u.s. consider two primary types of current; straight and alternating. A direct electric current (d. c.) flows through a conducting circuit in 1 management only. Information technology flows provided a straight voltage source is applied to the circuit.