Electric currents and their properties

Conduction is the name normally given to a movement or flow of charges. The charges are usually electrons, but may also be ions when the conduction takes place in gaseous or liquid conductors,, in which the ions are mobile.

How does the current flow through a wire? A metal is made up of tiny crystals which are visible under a microscope. A crystal is a regular and orderly arrangement of atoms. As it was explained, an atom is a complex particle in which tiny electrons move around nucleus. When the atoms are tightly packed as they are in a metallic solid, some of the electrons move freely between the atoms. These are called free electrons. Ordinarily, the free electrons move at random through the metal. There must be some driving force to cause the electrons to move through the metal conductor. This driving force tending to produce the motion of electrons through a circuit is called and electromotive force or e. m. f. that moves electric charges from one point in the circuit to another.

(When an electromotive force is applied to the ends of a wire the free electrons move in one direction. It is the movement of the free electrons in a conductor that induces an electric current. The greater the number of participating electrons, the greater is the flow of current.

No one has ever seen an electric current. We only know of the existence of a current by its effects. A current can heat a conductor, it can have a chemical action when passing through a solution, or it can produce a magnetic effect. We can measure currents by observing their heating, their chemical, or their magnetic effects.

There are some kinds of current, namely: a direct current (d. c, for short), an alternating current (a. c), a pulsating current.

NOTES AND COMMENTARY

a regular and orderly arrangement —правильне розташування атомів

at random — хаотично

driving force — рухаюча сила

e. m. f.— electromotive force — электрорухаюча сила, Э.Д.С. is applied to — приложена

It is the movement that — саме рух

the greater ... the greater — чим більше ... тим

d.c. = direct current — постійна напруга

for short — для скорочення

a. c. = alternating current — перемінна напруга

The Passive Voice

Present perfect

passive subject	'to be'	past participle
The resolution	has been	prepared
The delegates	have been	elected

Past perfect

passive subject	'to be'	past participle
The coat	had been	sold	by that time

Future perfect

passive subject	'to be'	past participle
He	will have been	examined	by next year

EXERCISE 1 Turn the following into the Passive Voice

1We turn on the light when it is dark. 2. The students finished their translation in time. 3. Helen washed the dishes. 4. Betty often took her younger brother for a walk. 5. Mother has made some coffee. 6. Have you ironed your dress yet? 7. Nina mispronounced this word. 8. They have told her the truth. 9. She promised us an interesting entertainment. 10. One uses chalk for writing on the blackboard. 11. I shall finish my work about seven o'clock. 12. Somebody has opened the door. 1.3. The waitress brought in the coffee. 14. One of my friends took me to the cinema last week. 15. We shall finish this work in time. 16. They built this house in 1960. 17. They were selling new children's books in that shop when I entered it yesterday. 18. Alarge group of young people joined us on our way to the station. 19. Ayoung teacher started a school in this village. 20. They are translating this article now. 21. Galsworthy wrote «The Forsyte Saga.» 21. Thousands of people attended this meeting. 22. He has just interrupted me. 23. The teacher has explained it to us.

EXERCISE 2 Turn the following into the Passive Voice

1. They did not invite her to the party. 2. I did not leave the window open. 3. They did not turn off the light. 4. I have invited some friends to tea 5. She has given me an English book. 6. Have you written the letter yet? 7. They have told us a lot оS interesting things. 8. The students have written the test-paper without mistakes. 9. The children have scattered about a lot of things. 10. The girl has put all the books into the bookcase. 11. Snov, will cover the fields in winter. 12. They will hand in the homework tomorrow. 13. I don't think we shall finish all the preparations today. 14. She al ways invites me to her dinner parties. 15. Shot showed me the dress which her daughter had made.16. We discussed the matter some days ago.17. Someone wants you on the phone. 18. She found my book on the window-sill. 19. They have built excellent shelters for tourists in these mountains. 20. Have you given the exercises to all the students? 21. The boy was angry because his mother did not allow him to go to the stadium. 22. Why have you put my books on this table?

EXERCISE 3 Turn the following into the Passive Voice

1. We received this letter after his departure. 2. Have dogs ever attacked you? 3. Bees gather honey from flowers. 4. The storm drove the ship against a rock. 5. Who discovered the circulation of blood? 6. They are selling delicious fruit ice cream there now. 7. The old man showed us the way out of the wood. 8. They offered her some interesting work. 9. The doctor prescribed her new medicine. 10. They often speak about him. 11. Everybody laughed at this funny animal. 12. We have been looking for you the whole morning. 13. We shall insist on strict discipline. 14. They teach three foreign languages at this school.

EXERCISE 4 Turn the following into the Active Voice

1. The light has not yet been turned off. 2. The boy was punished for misbehaving. 3. By three o'clock everything had been prepared. 4. The dictation was written without mistakes. 5. Whom was the poem written by? 6. Her dress was washed and ironed. 7. I was not blamed for the mistakes. 8. The papers had been looked through and corrected by the next lesson. 9. This house was built last year. 10. The letter has just been sent. 11. This article will be translated at the lesson on Tuesday. 12. When will this book be returned to the library? 13. The room was cleaned and aired. 14. Have all these books been read? 15. Whom were these letters written by? 16. The letter has just been typed. 17. She showed me the picture which had been painted by her husband. 18. I shall not be allowed to go there. 19. He has been told everything, so he knows what to do now. 20. All the questions must be answered. 21. The door has been left open. 22. Betty was met at the station. 23. The girl was not allowed to go to the concert.

24. She said that the new time-table had not yet been hung up on the notice-board. 25. The chicken was eaten with appetite. 26. It was so dark, that the houses could not be seen.

EXERCISE 5.Open the brackets using the verbs in the Passive Voice.

1. I am sure I (to ask) at the lesson tomorrow. 2. They told me that the new student (to speak) much about. 3. The hostess said that one more guest (to expect). 4. The newspaper said that an interesting exhibition (to open) in the Hermitage the next week. 5. This new dictionary (to sell) everywhere now. 6. All the texts (to look) through yesterday and not a single mistake (to find). 7. Two reports on Hemingway's stories (to make) in our group last month. Both of them were very interesting. 8. He said that Grandmother's letter (to receive) the day before. 9. Two new engineers just (to introduce) to the head of the department. 10. Don't worry, everything will be all right: the children (to take) to the theatre by the teacher and they (to bring) back to school in the evening.

EXERCISE 6 Change the following sentences into the Passive Voice.

Example: They have already brought the medicine. — The medicine has already been brought.

1. You have repaired our house lately. 2. When the fire brigade came, the fire had destroyed the building. 3. The athlete has shown much better results since this coach trains him, 4.1 will have answered all the business letters by noon. 5. The president of the board has signed the document. 6. Is she washing the floor? — No, she has already washed it. 1, By his arrival they had repaired his car. 8. He has booked the tickets and the clerk will have brought them by 2 o'clock. 9. They had painted the house by his arrival. 10. The police haven't found the reason for the accident yet. 11. Have you touched anything here? 12, The sociologist has interviewed a lot of students.13. Have they tested all the machines? 14. The flood has caused considerable damage, 15. John will have received the papers by tomorrow.

EXERCISE 7 Open the brackets and use the verb in the appropriate form of the Passive Voice

1, The first draft resolution (not discuss) yesterday; it (withdraw) long before the beginning of the meeting. 2. He is not in town; he (send) on a special mission, 3. Don't come into the compartment; the berth (fix) now. 4. A new underground line (construct) now. They say one of its stations (build) in my street. 5. He wants to know when the final decision (take). The activities of the committee and their delays already much (speak) about. 6. It was three o'clock. We (tell) to hurry up because we (wait). 7. Do you believe that such a problem can (solve)? 8. It must (do) without delays. 9. On September 9, 1850, California (admit) to the Union as the thirty-first state. 10. Don't speak in a loud voice: we (listen). 11. The plan (approve)? — No, it (discuss) now. — How long it (discuss)? 12. By the time he arrives everything (settle). 13. Not all the necessary things (buy) for our trip that's why the departure (postpone). 14. The money (lend) to him two months ago, but it (not give) back yet. 15. The business day was in high gear: the mail (look) through, documents (type), letters (answer), talks (hold). 16. Wait a minute. The table (lay). 17. Dynamite (invent) by Alfred Bernhard Nobel. 18. This exercise may (write) with a pencil. 19. This work (do) before you went to Poltava? 20. If you (ask) about it, will you be able to answer?

EXERCISE 8 Find and correct the mistakes if any,

1, Don't bring the article today. It will be being typed only tomorrow. 2. The South Pole was discovered by Amundsen in 1912, 3. The book which was written last month is discussing a lot. It has been written a lot of articles about. 4. When I came, an experiment was been holding in the lab. 5. Do you know that this house was belonged to Mr. Brown? 6. What new buildings have been built in your town since I was there? 7. The building was collapsed during the earthquake. 8. Have you seen him? Has he been changed much? 9. Do you know that you are following? 10.1 hope this journal can find at the library.

Lesson 6

Text 1 Read and translate the text pay attention to the new words

BASIC ELEMENTS OF HYDRAULIC SYSTEMS

The basic elements of hydraulic systems are:

1. The fluid.

2. The generator element (pump).

3. The transmission element (pipes and connections).

4. The control element (valve or restrictor).

5. The motor element (jack or continuous motor).

6. Tank and filter.

The most elementary form of pump can only function as a pump while the piston is moving into the cylinder and acts as a motor while the piston moves back. If non-return valves are added, the inlet valve is connected to a tank and the piston is given a to-and-fro motion, the device becomes a source

of continuous supply of liquid, except for interruptions during the suction stroke, which can be avoided by having two or more cylinders and pistons. Thus we obtain a continuous pump.

NOTES AND COMMENTARY

non-return valve —зворотній клапан to function as, to act as —функціонувати як

to and-fro motion –зворотно-поступовий рух