Electric current

 

An electric current is the flow of charges through a conducting circuit caused by a potential difference or electromotive force. In metallic conductors the charges are electrons. In liquids and gases the charges are ions. There are two types of electric current: direct current and alternating current. The current flowing in a circuit is DC if it flows continuously in one direction, and AC if it flows alternately in each direction. Current carries electrical energy from a power supply to the components of the circuit, where it is converted into other forms of energy. Electric current can heat a conductor, it can have a chemical action and it can produce magnetic effects. As compared to direct current, alternating current has several valuable characteristics. The most important of them is the fact that the voltage or the current may be varied to almost any desirable value by means of a transformer. AC is used as a source of electric power both in industry and in the home. The SI unit of electric current is the ampere. The volt is the SI unit of potential difference. The SI unit of electrical work is the watt. There are two basic types of electric circuits: series and parallel. In a series circuit the components of the circuit are arranged in such a way that they are connected end to end, so that the entire current passes through each component. The total resistance in such a circuit is the sum of the resistances of individual components. In parallel circuits the electric current flows through different pathways. Each branch of such a circuit can be switched on or off independently. This allows the use of some or all of the components by choice. In general, the total resistance of all components in parallel wiring is less than the resistance of any one of them. An electric circuit usually comprises two categories of components: active and passive. Passive elements never supply more energy than they absorb, while active elements can supply more energy than they absorb. Active components are: cells, batteries, generators, electron tubes, and transistors, etc. Passive components include: resistors, capacitors, inductors, relays, fuses, switches, etc.

 

Exercise 7. Answer the following questions.

 

1. What is an electric current? 2. What is the flow of charges through a circuit caused by? 3. What types of electric current are there? 4. How does direct current flow in a circuit? 5. Which current changes its direction? 6. What does electric current start to flow from? 7. When does electric current stop its flowing through a circuit? 8. What are the effects of electric current? 9. What is the most important characteristic of alternating current? 10. What is the function of a transformer? 11. What is the SI unit of electric current? 12. What is the SI unit of potential difference? 13. What is the watt? 14. What two basic types of electric circuits are there? 15. In what way are the circuit components arranged in a series circuit? 16. What is the total resistance in a series circuit? 17. How does the electric current flow in parallel circuits? 18. Can each branch of such a circuit be switched on or off independently? 19. What is the total resistance in a parallel circuit? 20. What components does an electric circuit comprise? 21. What components supply more energy than they absorb? 22. What are active components? 23. What do passive components include?

 

Exercise 8. Give Ukrainian / Russian equivalents to the following word combinations:

 

a) the flow of charges through a conducting circuit, the current flowing in a circuit, the SI unit of electric current (potential difference, electrical work), the total resistance in such a circuit, the sum of the resistances of individual components, each branch of such a circuit;

b) to be caused by a potential difference, to flow continuously in one direction, to flow alternately in each direction, to carry electrical energy from a power supply, to be converted into other forms of energy, to be connected end to end, to be varied to almost any desirable value, to be used as a source of electrical power.

Exercise 9. Give English equivalents to the following word combinations:

- металевий провідник - постійний струм - змінний струм - носії струму - джерело живлення - нагрівати провідник - коло (схема) з паралель-ним включенням - у порівнянні з - важлива характеристика - буль-яка потрібна величина - за допомогою трансформатора - як у промисловості, так і у домі - одиниця вимірювання у системі СІ - основні типи електрик-них кіл - кожний компонент - розташовуватися таким чином, що... - весь струм - взагалі (загалом)

- металлический проводник - постоянный ток - переменный ток - носители тока - источник питания - нагревать проводник - цепь (схема) с парал-лельным включением - по сравнению с - важная характеристика - любая требуемая величина   - при помощи трансформатора - как в промышленности, так и дома - единица измерения в системе СИ - основные типы электри-ческих цепей - каждый компонент - располагаться таким образом, что … - весь ток - вообще

 

Exercise 10. Form all possible verbal word combinations. Translate them.

1. to flow 2. to carry 3. to be converted 4. to heat 5. to produce 6. to be varied (to) 7. to be used 8. to be arranged 9. to be connected 10. to pass 11. to be switched on / off 12. to comprise 13. to supply

1. into other forms of energy 2. a conductor 3. magnetic effects 4. any desirable value 5. as a source of electric power 6. electrical energy 7. in one direction 8. end to end 9. in such a way that… 10. independently 11. through each component 12. more energy 13. two categories of components

 

Exercise 11. Put general and special questions to the following sentences.

 

1. Current carries electrical energy from a power supply to the components of the circuit. 2. Electric current can heat a conductor. 3. Alternating current has several valuable characteristics. 4. There are two basic types of electric circuits: series and parallel. 5. In parallel circuits the electric current flows through different pathways. 6. An electric circuit usually comprises two categories of components: active and passive.

 

Exercise 12. Fill in the blanks with prepositions and adverbs given below:

(Through, to, of, in, on, by, off, from)

1. An electric current is the flow … charges … a conducting circuit caused … a potential difference. 2. Current carries electrical energy … a power supply … the components … the circuit. 3. The current may be varied … almost any desirable value … means … a transformer. 4. … a series circuit the components … the circuit are arranged … such a way that they are connected end … end. 5. Each branch of such a circuit can be switched … or … independently. 6. This allows the use … some or all … the components … choice.

 

Exercise 13. Use the proper form of the verb in brackets.

 

1. An electric current (be) the flow of charges. 2. DC (flow) continuously in one direction. 3. Current (carry) electrical energy from a power supply. 4. Electric current (can heat) a conductor. 5. Alternating current (have) several valuable characteristics. 6. AC (be used) as a source of electric power. 7. An electric circuit usually (comprise) two categories of components: active and passive. 8. Passive elements never (supply) more energy than they absorb. 9. Passive components (include) resistors, capacitors, inductors, switches, etc.

 

Exercise 14. Write Past Indefinite and Past Participle forms of the following irregular verbs. Memorize them.

 

Be, have, do, find, give, take, go, come, know, learn, leave, lose, make, meet, put, read, see, show, speak, say, teach, tell, think, write.

 

Exercise 15. Give Past Participle forms of the following regular verbs. Mind the pronunciation of the ending.

 

a) [d]: cause, supply, carry, compare, arrange, vary, allow;

b) [t]: produce, pass, switch, place, develop, fix;

c) [id]: conduct, direct, convert, end, depend, heat, include.

 

Exercise 16. Group the following regular verbs according to the rules of ending pronunciation of regular verbs.

 

Charge, differ, force, type, continue, comprise, consist, connect, flow, resist, generate, combine, desire, work, end, absorb.

 

Exercise 17. Identify among the underlined words:

 

a) verbs: it flows, it will flow, a flow, its flow, the flow, does not flow;

b) participles: he knows, is known, he knew, the known effect, are charged, the charges;

c) nouns: a change, he changes, the changed direction, are changed, it changed; a flow of charges, the charged particle.

 

Exercise 18. Write out five verbs in the forms of the Present Indefinite Passive from the text.

 

Exercise 19. Indicate in which of the sentences the subject is active / passive.

 

1. The emitter emits current carriers. 2. Current carriers are emitted by the cathode. 3. Electric current can heat a conductor. 4. Potential difference is provided by a power source. 5. The potential difference is expressed in volts. 6. The alternating current changes its direction. 7. Voltage is measured in volts.

 

Exercise 20. Open the brackets using the verb

 

a) in the Present Indefinite Passive

1. All the elements of a complete electronic circuit (combine) on a single chip of semiconductor material. 2. The electron tubes (replace) by solid-state devices. 3. The current (vary) to almost any desirable value by a transformer. 4. The way the electric current flows through (call) a circuit. 5. Aeroplanes (classify) in different ways.

 

b) in the Present Indefinite Active or Passive

1. The aeroplane (propel) by a propeller or jet engine. 2. Flaps (increase) aerodynamic lift and drag and (use) during take-off and landing. 3. Metals (conduct) electricity with ease. 4. Substances through which electricity easily (transmit) (call) conductors. 5. Copper (carry) the current more freely than iron. 6. Rubber (not/allow) electricity to flow freely.

 

Exercise 21. Translate the following sentences into English.

 

Електричний струм – це потік зарядів по колу. Електричний струм тече, якщо є різниця потенціалів. В металевих провід-никах зарядами є електрони. В рідинах та газах заряди – іони. Існують два типи електричного струму – постійний та змінний.   Струм, що тече безперервно в одному напрямку, є постійним струмом. Струм, що тече поперемінно в кожному з напрямків, є змінним струмом. Змінний струм викорис-товується як джерело електричної енергії як в промисловості, так і в вдома. Існує два типи електричних кіл – послідовні і паралельні.   Електричне коло звичайно включає в себе активні та пасивні елементи. Пасивні елементи ніко-ли не віддають більшої кількості енергії, ніж вони поглинають Активні елементи мо-жуть віддавати більшу кількість енергії, ніж вони поглинають. Активні компоненти – це елементи, батареї, генератори, електронні лампи, транзистори та ін.   Пасивні елементи включають в себе резистори, конденсато-ри, котушки індуктив-ності, реле, електричні запобіжники, переми-качі та ін.

Электрический ток – это поток зарядов по цепи. Электрический ток течет, если есть разность потенциалов. В металлических проводниках заряды – электроны. В жидкостях и газах заряды – ионы. Существует два типа электрического тока – постоянный и переменный. Ток, который течет в одном направлении – постоянный ток.   Ток, который течет попеременно в каждом направлении – переменный ток. Переменный ток исполь-зуется, как источник электрической энергии как в промышленности, так и дома. Существует два типа электрических цепей – последовательные и параллельные. Электрическая цепь обычно включает в себя активные и пассивные элементы. Пассивные элементы никогда не отдают больше энергии, чем они поглощают. Активные элементы могут отдавать больше энергии, чем они поглощают. Активные компоненты - это элементы, батареи, генераторы, электрон-ные лампы, транзисторы и т.д.   Пассивные элементы включают в себя резис-торы, конденсаторы, катушки индуктивности, реле, электрические предохранители, перек-лючатели и т.д.

 

Exercise 22. Look through the text below and a) render it in English; b) make up dialogues on: – the types of electric current and its properties; - the electric circuit and its components.

The Electric Circuit and its Properties

Electric current is a movement of electrons and ions. There are two kinds of electric current: alternating current (a.c) and direct current (d.c.).

Alternating current is a to and fro movement of electrons or ions. Direct current is a directed movement of electrons or ions.

Electric current flows only when there is a potential difference. Potential difference is provided by a power source (a battery or a generator).

The way along which an electric current flows is called a circuit. Electric current has heating, mechanical, chemical, and magnetic effects. We measure voltage (or potential difference) in volts, the rate of current flow in amperes and the power in watts. We measure resistance to current flow in ohms.

 

Exercise 23. Find sentences with the verbs “to be” and “to have” in the text. State their functions.

 

Exercise 24. Identify the tense and voice of the verbs in the sentences of the text.

 

Exercise 25. Speak on: - the types of electric current and electric current properties; - the electric circuit and its components.