Exercise 1. According to the models given below form sentences combining suitable parts of the sentences given in columns I, II, III, IV

Model: a) The current is known to consist of moving electrons.

I II III IV

1. Lomonosov 1. was observed 1. to have started 1.in English speaking countries

2. Electrical 2. is said 2. to attract and hold 2. for Moscow on foot

3. The Fahrenheit 3. is known 3. to be used 3. minute light objects after

scale rubbing

 

Model: b) We known lightning to be a discharge of electricity.

I II III IV

1. We know 1. the alternating current 1. to be 1. first in one direction and then in another

2. static electricity 2. to flow 2. important effects

3. the charges 3. to produce 3. positive and negative

 

Exercise 2. Choose the sentences with: a) the Subjective Infinitive Construction; b) the Objective Infinitive Construction. Translate them into Ukrainian / Russian.

1.The current is known to flow when the circuit is closed. 2. To stop the current flow is to break the circuit in some point. 3. To stop the current flow you must open the circuit. 4. A fuse is expected to melt and break the circuit. 5. Various switches are used to open or to close a circuit. 6. A switch is a device to break or to close the circuit. 7. We know the circuit to be a path of an electric circuit. 8. We may expect a short circuit to result from wire fault. 9. The overloading of the line is likely to produce a short circuit. 10. Electromotive force in necessary for the current to flow along the circuit. 11. Ampere supposed the current to flow from the positive pole of the source to the negative pole. 12. We know the electron to be a minute particle having an electric charge.

 

III. Reading.

Exercise 1. Read and translate the text.

Text A.

ELECTRIC CURRENT

Ever since Volta first produced a source of continuous current, men of science have been forming theories on this subject. For some time they could see no real difference between the newly-discovered phenomenon and the former understanding of static charges. Then the famous French Scientist Ampere (after whom the unit of current was named) determined the difference between the current and the static charges. In addition to it, Ampere gave the current direction: he supposed the current to flow from the positive pole of the source round the circuit and back again to the negative pole.

We consider Ampere to be right in his first statement but he was certainly wrong in the second, as to the direc­tion of the current. The student is certain to remember that the flow of current is in a direction opposite to what he thought.

Let us turn our attention now to the electric current itself. The current which flows along wires consists of mov­ing electrons. What can we say about the electron? We know the electron to be a minute particle having an elec­tric charge. We also know that that charge is negative. As these minute charges travel along a wire, that wire is said to carry an electric current.

In addition to traveling through solids, however, the electric current can flow through liquids as well and even through gases. In both cases it produces some most impor­tant effects to meet industrial requirements.

Some liquids, such as melted metals for example, conduct current without any change to themselves. Others, called electrolytes, are found to change greatly when the current passes through them.

When the electrons flow in one direction only, the cur­rent is known to be d. c, that is, direct current. The sim­plest source of power for the direct current is a battery, for a battery pushes the electrons in the same direction all the time (i.e., from the negatively charged terminal to the positively charged terminal).

The letters a.c. stand for alternating current. The cur­rent under consideration flows first in one direction and then in the opposite one. The a.c. used for power and light­ing purposes is assumed to go through 50 cycles in one sec­ond. One of the great advantages of a.c. is the ease with which power at low voltage can be changed into an almost similar amount of power at high voltage and vice versa. Hence, on the one hand alternating voltage is increased: when it is necessary for long-distance transmission and, on the other hand, one can decrease it to meet industrial re­quirements as well as to operate various devices at home.

Although there are numerous cases when d.c. is re­quired, at least 90 percent of electrical energy to be gen­erated at present is a.c. In fact, it finds wide application for lighting, heating, industrial, and some other purposes.

One cannot help mentioning here that Yablochkov, Rus­sian scientist and inventor, was the first to apply a.c. in practice.

 

IV. Language.

Exercise 1. Find the correspondence.

1. to increase voltage 2. negative terminal 3. opposite direction 4. electrical wires 5. charged particles 6. to meet industrial requirement 7. important statements 8. wide application 9. battery terminal 10. steel wire 11. minute particles

1. маленькі частинки 2. важливе ствердження (утвердження) 3. задовольняти вимоги промисловості 4. протилежний напрямок 5. стальний провід 6. збільшувати напругу 7. заряджені частинки 8. електричні проводи 9. негативно заряджена клема 10. широке використання 11. клема батареї

 

Exercise 2. Form six sentences combining suitable parts of the sentences given n columns I and II.

I II

1. The electric current is 1. The energy of position

2. kinetic energy is 2. electricity at rest

3. static electricity is 3. the flow of moving

4. Potential energy is 4. the energy of motion

5. The direct current is 5. a discharge of electricity

6. Lighting is 6. the flow of electrons in one direction

7. The alternating current is 7. the flow of electrons in one direction and then in the opposite one.

 

V. Comprehension.

Exercise 1. Find the wrong statements and correct them:

1. Electrons flow from the positively charged terminal of the battery to the negatively charged terminal.

2. Ampere supposed the current to flow from the negative pole to the positive one.

3. Static electricity is used for practical purposes.

4. Static electricity is not very high in voltage and it is easy to control it.

5. The direct current is known to flow first in one direction and then in the opposite one.

6. The direct current used for power and lighting purposes is assumed to do through 50 cycles a second.

 

Exercise 2. Answer the following questions:

1. Who first produced a source of continuous current?

2. After whom was the unit of current named?

3. Who determined the difference between the current and the static charges?

4. What did Ampere suppose?

5. When does a wire carry an electric current?

6. What can you say about electrolytes?

7. What do you call d.c.?

8. What is the advantage of a.c.?

9. Where is a.c. used?

10. Who first applied a.c.?

 

VI. Practice.

Exercise 1. Ask you group-mates the following questions. Let him / her answer them:

1. If electricity is a form of energy;

2. If there are two types of electricity;

3. If alternating voltage can be increased and decreased;

4. If Ampere determined the difference between the current and the static charges;

5. If the electric current can flow through liquids and through gases;

6. If the electrolytes change greatly when the current passes through them;

7. If a negatively charged electron will move to the positive end of the wire.

 

Exercise 2. Explain why:

1. static electricity cannot be used to light lamps, to boil water, and so on;

2. voltage is increased or decreased;

3. the unit of electric preassure is called volt;

4. Ampere was wrong as to the current direction;

5. the current is said to flow from the positive end of the wire to its negative end.

 

Exercise 3. Use the plan to speak about Electric Current:

1. Ampere`s supposition as to the current direction.

2. Electron and electric charge.

3. Substances, electric current can flow through.

4. D.c. and a.c. current.

 

VII. Reading and practice.

Exercise 1. Read the text B in 7 minutes without a dictionary and answer the question “What is discussed in the present text?”

Text B.

ELECTRIC CIRCUIT

The electric circuit is the subject to be dealt with in the present article. But what does the above term really mean? We know the circuit to be a complete path which carries the current from the source of supply to the load and then carries it again from the load back to the source.

The purpose of the electrical source is to produce the necessary electromotive force required for the flow of current through the circuit.

The path along which the electrons travel must be com­plete otherwise no electric power can be supplied from the source to the load. Thus we close the circuit when we switch on our electric lamp.

If the circuit is broken or, as we generally say "opened" anywhere, the current is known to stop everywhere. Hence, we break the circuit when we switch off our electrical devices. Generally speaking, the current may pass through solid conductors, liquids, gases, vacuum, or any combination of these. It may flow in turn over transmission lines from the power-station through transformers, cables and switches, through lamps, heaters, motors and so on.

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. 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 your room and your house are generally connected in parallel.