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) електричні кола, 2) электричний заряд, 3) провідник, 4) опір, 5) рух електронів, 6) ізолятор, 7) коротке замикання, 8) енергія. 

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? 

VII. Talk on the types of electric circuits