Text 6

Pre-reading practice:

1. What do you know about the electric circuit?
2. Are all circuits similar?

Electric Circuits The concepts of electric charge and potential are very important in the study of electric currents. When an extended conductor has different potentials at its ends, the free electrons of the conductor itself are caused to drift from one end to the other. The potential difference must be maintained by some electric source such as electrostatic generator or a battery or a direct current generator. The wire and the electric source together form an electric circuit, the electrons are drifting around it as long as the conducting path is maintained. There are various kinds of electric circuits such as: open circuits, closed circuits, series circuits, parallel circuits and short circuits. To understand the difference between the following circuit connections is not difficult at all. If the circuit is broken or «opened» anywhere, the current is known to stop everywhere. The circuit is broken when an electric device is switched off. The path along which the electrons travel must be complete otherwise no electric power can be supplied from the source to the load. Thus the circuit is “closed” when an electric device is switched on. When electrical devices are connected so that the current flows from one device to another, they are said «to be connected in series». Under such conditions the current flow is the same in all parts of the circuit as there is only a single path along which it may flow. The electrical bell circuit is considered to be a typical example of a series circuit. The “parallel” circuit provides two or more paths for the passage of current. The circuit is divided in such a way that part of the current flows through one path and part through another. The lamps in the houses are generally connected in parallel. The “short” circuit is produced when the current can return to the source of supply without control. The short circuits often result from cable fault or wire fault. Under certain conditions the short circuit may cause fire because the current flows where it was not supposed to flow. If the current flow is too great a fuse is used as a safety device to stop the current flow.

Practice 1. Re-read the text and answer the questions.

1. What kinds of electric circuits do you know?

2. How do closed and open circuits differ?

3. When do we say that electrical devices are connected in series?

4. What kind of a circuit provides two or more paths for the passage of current?

5. The “short” circuit is produced when the current can return to the source of supply without control, isn’t it?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

- extended conductor;

- potential difference;

- to be maintained by;

- open circuits; - closed circuits; - series circuits; - parallel circuits; - short circuits.

Practice 3. Match up the words with their definitions

Maintain разнообразные

connection путь

various поддерживать

path поток

flow делить

divide связь

Practice 4. Complete the sentences using the words from the table:

The “short” circuit is produced	open circuits, closed circuits, series circuits, parallel circuits and short circuits.
There are various kinds of electric circuits such as	when the current can return to the source of supply without control.
To understand the difference between the following circuit connections	the current is known to stop everywhere.
If the circuit is broken or «opened» anywhere,	is not difficult at all.

Practice 5. Complete the table:

Verb	noun	adjective or participle
	connection
		various
Divide
suppose

Text 7

Pre-reading practice:

1. Do you think all matters have similar ability to conduct the electric current?2. What does this ability depend on? CONDUCTORS AND INSULATORS All substances have some ability of conducting the electric current, however, they differ greatly in the ease with which the current can pass through them. Solid metals conduct electricity with ease while non-metals do not allow it to flow freely. Thus, there are conductors and insulators.What do the terms "conductors" and "insulators" mean?This difference is expressed by what is called electrical conductivity of the body. It depends upon the atomic constitution of the body. Substances through which electricity is easily transmitted are called conductors. Any material that strongly resists the electric current flow is known as an insulator.There is a great difference in the conducting ability of various substances. Almost all metals are good electric current conductors. The best conductors are silver, copper, gold and aluminum. Nevertheless, copper carries the current more freely than iron; and silver, in its turn, is a better conductor than copper.Copper is the most widely used conductor. The electrically operated devices are connected to the wall socket by copper wires.A material which resists the flow of the electric current is called an insulator.The higher the opposition is, the better the insulator is. There are many kinds of insulation used to cover the wires. The kind used depends upon the purposes the wire or cord is meant for. The insulating materials generally used to cover the wires are rubber, asbestos, glass, plastics and others. The best insulators are oil, rubber and glass.Rubber covered with cotton, or rubber alone is the insulating material usually used to cover desk lamp cords and radio cords.Glass is the insulator to be often seen on the poles that carry the telephone wires in city streets. Glass insulator strings are usually suspended from the towers of high voltage transmission lines. One of the most important insulators of all, however, is air. That is why power transmission line wires are bare wires depending on air to keep the current from leaking off.Conducting materials are by no means the only materials to play an important part in electrical engineering. There must certainly be a conductor, that is a path, along which electricity is to travel and there must be insulators keeping it from leaking off the conductor.

Practice 1. Re-read the text and answer the questions.

1. In what a way do substances differ?

2. What are conductors and insulators?

3. What are the best conductors?

4. What are the best insulators?

5. Why are power transmission line wires bare ones?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

- to conduct electricity;

- to flow freely;

- to be expressed by;

- atomic constitution;

- conducting ability;

- electrically operated devices;

- kinds of insulation;

- power transmission line wires.

Practice 3. Match up the words with their definitions

substance медь

transmit выражать

copper веществоcover передавать rubber резинаexpress покрывать

Practice 4. Complete the sentences using the words from the table:

A material which resists the flow of the electric current	however, they differ greatly in the ease with which the current can pass through them.
All substances have some ability of conducting the electric current	used to cover the wires.
The higher the opposition is,	is called an insulator.
There are many kinds of insulation	the better the insulator is.

Practice 5. Complete the table:

verb	noun	adjective or participle
express
insulate
		keeping
receive	transmission

Text 8

Pre-reading practice:

1. What do you know about the nature of semiconductors?
2. How do they differ from conductors?

SEMICONDUCTORS There are materials that really occupy a place between the conductors of the electric current and the non-conductors. They are called semiconductors.These materials conduct electricity less readily than conductors but much better than insulators. Semiconductors include almost all minerals, many chemical elements, a great variety of chemical compounds, alloys of metals, and a number of organic compounds. Like metals, they conduct electricity but they do it less effectively. In metals all electrons are free and in insulators they are fixed. In semiconductors electrons are fixed, too, but the connection is so weak that the heat motion of the atoms of a body easily pulls them away and sets them free. Heat is by no means the only phenomenon influencing semiconductors. They are sensitive to light, too. Just as they are influenced by falling light, semiconductors are also influenced by all radiation. Generally speaking, they are so sensitive that a heated object can be detected by its radiation. Such dependence of conductivity on heat and light has opened up great possibilities for various uses of semiconductors. The semiconductor devices are applied for transmission of signals, for automatic control of a variety of processes, for switching on engines, for the reproduction of sound, protection of high-voltage transmission lines, speeding up of some chemical reactions, and so on. On the one hand they may be used to transform light and heat energy directly into electric energy without any complex mechanism with moving parts, and on the other hand, they are capable of generating heat or cold from electricity. Russian engineers and scientists turned their attention to semiconductors many years ago. They saw in them a means of solving an old engineering problem, namely, that of direct conversion of heat into electricity without boilers or machines. Semiconductor thermocouples created in Russia convert heat directly into electricity just as a complex system consisting of a steam boiler, a steam engine and a generator does it.

Practice 1. Re-read the text and answer the questions.

1. What are semiconductors?

2. What do semiconductors include?

3. What are semiconductors influenced by?

4. What are semiconductor devices applied for?

5. Why did Russian engineers turn their attention to semiconductors?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

- less readily;

- chemical compounds;

- heat motion;

- to be applied for;

- to be sensitive to smth.;

- on the one (other) hand;

- to turn attention to smth.

-

Practice 3. Match up the words with their definitions

Include толкать

compound зависимость

pull включатьdependence соединениеpossibility возможностьengine двигатель

Practice 4. Complete the sentences using the words from the table:

Heat is by no means the only phenomenon	has opened up great possibilities for various uses of semiconductors.
. In metals all electrons are free	influencing semiconductors.
Such dependence of conductivity on heat and light	and in insulators they are fixed.
These materials conduct electricity less readily than conductors	but much better than insulators.

Practice 5. Complete the table:

verb	noun	adjective or participle
	influence
include
		sensitive
turn

Text 9

Pre-reading practice:

1. Do you know any machines which convert one kind of energy into another?
2. What do you know about dinamos?

DYNAMOS The term «dynamo» is applied to machines which convert either mechanical energy into electrical energy or electrical energy into mechanical energy by utilizing the principle of electromagnetic induction. A dynamo is called a generator when mechanical energy supplied in the form of rotation is converted into electrical energy. When the energy conversion takes place in the reverse order the dynamo is called a motor. Thus a dynamo is a reversible machine capable of operation as a generator or motor as desired. A generator does not create electricity, but generates or produces an induced electromotive force, which causes a current to flow through a properly insulated system of electrical conductors external to it. The amount of electricity obtainable from such a generator is dependent upon the mechanical energy supplied. In the circuit external to a generator the e. m. f. causes the electricity to flow from a higher or positive potential to a lower or negative potential. In the internal circuit of a generator the e. m. f. causes the current to flow from a lower potential to a higher potential. The action of a generator is based upon the principles of electromagnetic induction. The dynamo consists essentially of two parts: a magnetic field, produced by electromagnets, and a number of loops or coils of wire wound upon an iron core, forming the armature. These parts are arranged so that the number of the magnetic lines of force of the field threading through the armature, coils will be constantly varied, thereby producing a steady e. m. f. in the generator or a constant torque in the motor.

Practice 1. Re-read the text and answer the questions.

1. What is the term “dynamo” applied to?

2. What kind of a generator is called dynamo?

3. What kind of a generator is called a motor?

4. How many parts does dynamo consists of?

5. How are these parts arranged?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

- electromagnetic induction;

- energy conversion;

- a reversible machine;

- induced electromotive force;

- insulated system;

- to be dependent upon;

- internal circuit;

- coils of wire;

- iron core.

Practice 3. Match up the words with their definitions

сonvert создавать

Utilizе количество

create поставлять

amount катушкаsupplу превращатьcoil использовать

Practice 4. Complete the sentences using the words from the table:

A generator does not create electricity	a magnetic field, produced by electromagnets, and a number of loops or coils of wire wound upon an iron core, forming the armature.
The term «dynamo» is applied to machines	but generates or produces an induced electromotive force.
The dynamo consists essentially of two parts	is based upon the principles of electromagnetic induction.
The action of a generator	which convert either mechanical energy into electrical energy or electrical energy into mechanical energy by utilizing the principle of electromagnetic induction.

Practice 5. Complete the table:

Verb	noun	adjective or participle
	supply
Utilize
		convertable
Create

Text 10

Pre-reading practice:

1. What do you know about the functios of transformers?2. What is practical application of transformers? TRANSFORMERS One of the great advantages in the use of the alternating current is the ease with which the voltage may be changed by means of a relatively simple device known as a transformer. Although there are many different types of transformers and a great variety of different applications, the principles of action are the same in each case. The transformer is a device for changing the electric current from one voltage to another. It is used for increasing or decreasing voltage. So the function of a transformer is to change voltage and current of an alternating system to meet requirements of the equipment used. It is known to be simple in elementary principle, and in construction that is it involves no moving parts. Transformers change voltage through electro-magnetic induction. The principle parts of a transformer are: an iron core and, usually, two coils of insulated windings. One of them is called primary, another is called the secondary. The primary coil is connected to the source of power. The secondary coil is connected to the load. Thus, the primary is the coil to which power is supplied. The secondary is the coil from which power is taken. In scientific terms to produce an alternating magnetic flux in the iron core an alternatingcurrent must be passed through the primary coil. This flux is considered to induce electromotive force in both primary and secondary coils. The secondary coil is open – circuited. Current flows in the secondary coil when the latter is connected to the external circuit or load. The flow of current in the secondary coil tends to reduce the flux in the core. Transformers are placed inside a steel tank usually with oil to improve the insulation and also to cool the device.

Practice 1. Re-read the text and answer the questions.

1. What is a transformer?

2. What is the function of a transformer?

3. How is a transformer constructed?

4. In what case is an alternating magnetic flux produced?

5. Where are transformers placed and what for?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

- great advantages;

- by means of;

- different applications;

- increasing (decreasing) voltage;

- primary (secondary) coils;

- to induce electromotive force;

- to improve the insulation.

Practice 3. Match up the words with their definitions

advantage улучшать

ease применениеapplications требованиеrequirement грузload легкостьimprove применение

Practice 4. Complete the sentences using the words from the table:

The principle parts of a transformer are	is connected to the load.
The transformer is a device	an iron core and, usually, two coils of insulated windings.
Transformers change voltage	through electro-magnetic induction.
The secondary coil	for changing the electric current from one voltage to another.

Practice 5. Complete the table:

verb	noun	adjective or participle
	requirement
apply
		easy
improve

PART II Text 1.

Practice 1. Choose the key sentence in each paragraph.

Practice 2. Re-read the text to find out the author’s main idea:

1. Researchers are working on a thermoelectric generator that converts the heat from car exhaust fumes into electricity.

2. In an age of dwindling natural resources, energy-saving is the order of the day.

3. The new generator will cut fuel consumption and help reduce the CO₂ emissions from motor vehicles.

4. Many technical processes use less than one-third of the energy they employ.

Practice 3. Make a review of the text.