VIII. Say some sentences about the types of electric current and its properties.

Unit 3

I. Read the text.

Effects produced by a current

The current flow is detected and measured by any of the effects that it produces. There are three important effects accompanying the motion of electric charges: the heating, the magnetic, and chemical effects, the latter is manifested under special conditions.

The production of heat is perhaps the most familiar among the principal effects of an electric current. The heating effect of the current is found to occur in the electric circuit itself. It is detected owing to an increase in the temperature of the circuit. This effect represents a continual transformation of electric energy into heat. For instance, the current which flows through the filament of an incandescent lamp heats that filament to a high temperature.

The heat produced per second depends both upon the resistance of the conductor and upon the amount of current carried through it. The thinner the wire is, the greater the developed heat is. On the contrary, the larger the wire is, the more negligible the heat produced is. Heat is greatly desirable at times but at other times it represents a waste of useful energy. It is this waste that is generally called " heat loss" for it serves no useful purposes and decreases efficiency.

The heat developed in the electric circuit is of great practical importance for heating, lighting and other purposes. Owing to it people are provided with a large number of appliances, such as: electric lamps that light our homes, streets and factories, electrical heaters that are widely used to meet industrial requirements, and a hundred and one other necessary and irreplaceable things which have been serving mankind for so many years.

The electric current can manifest itself in some other way. It is the motion of the electric charges that produces the magnetic forces. A conductor of any kind carrying an electric current, a magnetic field is set up about that conductor. This effect exists always whenever an electric current flows, although in many cases it is so weak that one neglects it in dealing with the circuit. An electric charge at rest does not manifest any magnetic effect. The use of such a machine as the electric motor has become possible owing to the electromagnetic effect.

The last effect to be considered is the chemical one. The chemical effect is known to occur when an electric current flows through a liquid. Thanks to it a metal can be transferred from one part of the liquid to another. It may also effect chemical changes in the part of the circuit comprising the liquid and the two electrodes which are found in this liquid. Any of the above mentioned effects may be used for detecting and measuring current.

II. Give the English equivalents for the following words:

1) выявлять, обнаруживать	6) лампа накаливания
2) измерять	7) прибор
3) заряд	8) потеря энергии
4) нить накала	9) освещать
5) тепловой эффект	10) обнаруживаться, проявляться

III. Guess the meaning of the following international words:

transformation, temperature, chemical, magnetic, special, practical, motor, electrode.

IV. Insert words and expressions:

1. The current flow is (выявляется и измеряется) by any of the effects that it produces.

2. There are three important effects accompanying the motion of (электрические заряды).

3. The current which flows through the (нить накала лампы накаливания) heats that filament to a high temperature.

4. Heat represents (потерю полезной энергии) at times.

5. Electric lamps (освещать) our homes, streets and factories.

6. The electric current can (проявлять) magnetic effect.

V. Choose the correct translation:

The heating effect of the current is found to occur in the electric circuit itself.

1. Установлено, что тепловой эффект электрического тока появляется в самой электрической цепи.

2. Тепловой эффект электрического тока может появляться в самой электрической цепи.

3. Установлено, что тепловой эффект электрического тока должен появляться в самой электрической цепи.

Когда в любом проводнике появляется электрический ток, вокруг него возникает магнитное поле.

1. A conductor of any kind carrying an electric current, a magnetic field was set up about that conductor.

2. A conductor of any kind have been carrying an electric current, a magnetic field is set up about that conductor.

3. A conductor of any kind carrying an electric current, a magnetic field is set up about that conductor.

Последний эффект, который необходимо рассмотреть – химический эффект.

1. The last effect is considered to be the chemical one.

2. The last effect to be considered is the chemical one.

3. The last effect would be considered the chemical one.

Известно, что химический эффект возникает, когда электрический ток проходит через жидкость.

1. The chemical effect is known to occur when an electric current flows through a liquid.

2. The chemical effect is famous to occur when an electric current flows through a liquid.

3. The chemical effect may be known to occur when an electric current flows through a liquid.

Именно движение электрических зарядов порождает магнитные силы.

1. The motion of the electric charges produces the magnetic forces.

2. It is the motion of the electric charges that produces the magnetic forces.

3. The motion of the electric charges is certain to produce the magnetic forces.

VI. Answer the questions:

1. What effects does the current flow produce?

2. How is the heating effect detected?

3. What does the heat produced depend upon?

4. What is called “heat loss”?

5. How is the magnetic effect set up?

6. What is the main condition of the magnetic effect existence?

7. When does the chemical effect occur?

VII. Fill in the chart:

Electric current effect	Practical application
1. heating effect 2. ….. 3. chemical effect	….. use of electric motor …..

VIII. Speak about the principal effects of an electric current, using the text and chart above.

UNIT 4

I. Read the text.

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.

II. Guess the meaning of the following international words:

concept, potential, electrostatic generator, aluminum, parallel, typical, control.

III. Give the English equivalents for the following words and word combinations:

1) электрические цепи, 2) электрический заряд, 3) проводник, 4) сопротивление, 5) движение электронов, 6) изолятор, 7) короткое замыкание, 8) энергия.

IV. Say whether these sentences are true or false:

1. When an extended conductor has the same potential at its ends, free electrons are drifting from one end to another.

2. The wire and the electric source together form an electric circuit.

3. A path of any material will allow current to exist.

4. Silver, copper and gold oppose very strongly.

5. The slighter the opposition is, the better the insulator is.

6. There is only one type of electric circuit.

7. We close the circuit when we switch on our electric device.

V. Complete the sentences using the text:

1. The potential difference must be maintained by …

2. Materials that offer slight opposition are called …

3. The best insulators are …

4. There are various kinds of electric circuits such as …

5. We “open” the circuit when …

6. We “close” the circuit when …

7. The “short” circuit is produced when …

8. A fuse is …

VI. Answer the questions:

1. What concepts are very important in study of electric current?

2. What forms an electric circuit?

3. What materials are the best conductors and insulators?

4. What kinds of electric circuits do you know?

5. How can we open and close the circuit?

6. When are electrical devices connected in series?

7. What is an example of a series circuit?

8. What can you say about “parallel” circuits?

9. What does the short circuit often result from?

⇐ Предыдущая 123 4 5 6 7 8 9 10 Следующая ⇒