Text 2. Types of electric current

As we have learned, some kinds of atoms contain loosely attached electrons. Electrons are made to move easily from one atom to another. When those electrons move freely between the atoms of matter, a current of electricity is created.

Some things conduct electricity better than others. The property of some things to conduct electricity is called their resistance. Resistance in a wire depends on how thick and how long it is, and what it’s made of.

Different types of metal are used in making wires. You can have copper wire, aluminum wire, even steel wire. Each of these metals has a different resistance. The lower the resistance of a wire, the better it conducts electricity.

Copper is used in many wires because it has a lower resistance than many other metals. The wires in your walls, inside your lamps and elsewhere are usually copper.

A piece of metal can be made to act like a heater. When an electric current occurs, the resistance causes friction and the friction causes heat. The higher the resistance, the hotter it can get.

Some things conduct electricity very poorly. These are called insulators. Rubber is a good insulator, and that’s why rubber is used to cover wires in an electric cord. Glass is another good insulator. Іf you look at the end of a power line, you’ll see that it is attached to some bumpy looking things. These are glass insulators. They keep the metal of the wires from touching the metal of the towers.

To compare electric currents we should have certain units by means of which they are to be measured. The practical unit of current is called the ampere. The practical unit of resistance is called the ohm. This unit can be defined as the relation between the difference of potential and the current that flows in a conductor.

There are two common types of electric current: direct an alternating. A direct current (d.c.) flows continuously through a conducting circuit in one direction only. An alternating current (a.c.) continually reverses in direction. A direct current is the flow of electrons that starts from a battery or generator, passes through resistances, meters, motors and so on, and finally returns to its starting point. A direct current is used in the electrical system of an automobile and an airplane, in a tram, telegraph, telephone, in industry, etc. However, at present another type of electric current is used for lighting, heating and industrial purposes. This current flowing first in one direction and then in another is called an alternating current. The alternating current has one great advantage. Using a transformer, it is possible to transform power at low voltage into high voltage power and back again. Power is transmitted over long distances with less loss at high voltage than at low voltage. The alternating current supplies the greatest part of electric power for industry today. Having more insulation the high voltage cable is much more cheaper than the large low voltage cable. Being cheaper, high voltage is therefore essential for the economical transmission of electric power.

 

Exercise 15. Define the parts of speech and translate the words.

a) insulate – insulator; measure – measurement; conduct – conductor; resist – resistance; heat – heater; differ – difference; direct – direction; transform – transformer; transmit – transmission; generate – generator;

b) loose – loosely; usual – usually; free – freely; easy – easily; poor – poorly; continuous – continuously; final – finally; practical – practically; potential – potentially; alternative – alternately.

 

Exercise 16. Give the initial form of the following words. Define the parts of speech and translate.

Better, lower, higher, hotter, less, greatest, cheaper, more.

 

Exercise 17. Translate and comment upon the following grammar forms.

Are made; is created; conducts; is called; are used; can have; can be made; should have; are to be; reverses; is transmitted; being cheaper; having more; is much more cheaper; made of.

Exercise 18. Match the English-Ukrainian equivalents.

1) current 2) resistance 3) conductor 4) wire 5) insulator 6) tower 7) potential 8) transformer 9) voltage 10) heater

a) нагрівач b) ізолятор c) струм d) трансформатор e) напруга f) провідник g) опір h) вежа i) дріт j) потенціал

 

Exercise 19. Translate the following universal words without a dictionary. Mind their pronunciation.

Atom, electron, electricity, metal, aluminum, steel, lamp, line, ohm, start, motor, generator, automobile, telegraph, telephone, industry, battery.

 

Exercise 20. Translate the following word combinations into Ukrainian.

Current of electricity; resistance of wire; potential difference; glass insulator; metallic heater; metallic conductor; practical unit; electric current; direct current; alternating current; starting point; industrial purpose; low voltage; high voltage; high voltage cable; electric power; economical transmission; conducting circuit.

 

Exercise 21. Complete these sentences using English equivalents of the words in brackets.

1. When (електрони) move freely between the (атоми) of matter, a (струм) of electricity is created. 2. The (вимірювання) how well something conducts electricity is called its (опір). 3. A piece of metal can be made to act like a (нагрівач). 4. Glass is a good (ізолятор). 5. A (постійний струм) flows continuously through a (провідникове коло) in one direction only. 6. The current flowing first in one direction and then in another is called an (змінний струм). 7. Having more insulation a (кабель високої напруги) is much more cheaper than a large (кабель низької напруги).

 

Exercise 22. Give terms to the following definitions.

1. The flow of electrons through a conductor under the action of an electric force. 2. The property of some things to conduct electricity.

3. The things conducting electricity very poorly. 4. The practical unit of resistance. 5. The practical unit of current. 6. Current flowing continuously in one direction. 7. Current flowing alternately in each direction. 8. The current which supplies the electric power over long distances with less loss at high voltage. 9. The device to transform power at low voltage into high voltage power and back again. 10. The voltage which is essential for the economical transmission of electric power.

 

Exercise 23. Translate the following questions and answer them.

1. Як утворюється електричний струм? 2. Що називають опором провідника? 3. Від чого залежить провідність матеріалів? 4. Які матеріали називають ізоляторами? 5. Які одиниці виміру застосовують для вимірювання струму та опору? 6. Який струм протікає безперервно в одному напрямку? 7. Який струм називають змінним струмом? 8. Який струм, постійний чи змінний, використовують у промислових цілях? 9. Яку перевагу має змінний струм у порівнянні з постійним струмом? 10. Які кабелі застосовують для передачі електроенергії на великі відстані?

 

Exercise 24. Learn the following words and word combinations.

Circuit – схема, коло (в електриці)

bridge – місток, перемичка

destroy – руйнувати

attract – притягувати

filament – катодна нитка, нитка розжарення (накалювання)

bulb – електрична лампа

glow – жар, розжарення

collide – зіштовхуватись

reverse – змінювати на протилежний; повністю змінювати

set (up) – облаштований

scattering – розсіювання

switch – перемикач

break – пошкоджувати

rush – хлинути, кидатися

series – послідовна (схема), з послідовним підключенням

parallel – паралельна (схема), з паралельним підключенням

wind (past, p.p. wound) – намотувати(ся)

suspend – підвішувати

coil – котушка (індуктивності); намотувати, обмотувати

coiled (up) – звернений у кільце, укладений у спіраль (про дріт)

field – поле

repulse – відштовхуватись (один від одного)

spin – обертати(ся)

 

Exercise 25. Read and translate text 3.