Lesson 4. Topic Electric current Grammar material: The Passive Voice. Text : Electric current Ever since Volta first produced a source of continuous

Transcription

1 Lesson 4. Topic Electric current Grammar material: The Passive Voice. Text : 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 travelling 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

2 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 per cent 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. TEST. Electric current. I. Put the questions to the words underlined: 1. French scientist Ampere determined the difference between the current and the static charges. 2. Volta produced a source of steady continuous current in The current can flow through liquids as well as through solids. 4. The electron is a minute particle having an electric charge. II. Connect the word combinations: newly discovered static positive industrial alternating wide Russian vice application charges pole versa current requirements inventor phenomenon III. Find the right meaning. a.c _? 1. when the electrons flow in one direction only. d.c? 2. when the current flows first in one direction and then in the opposite one.

3 IV. Write the antonyms for: 1. to be wrong 2. positive 3. big 4. liquid 5. discharge 6. disadvantage 7. high 8. on the other hand 9. to decrease. V. Connect the first part of the sentence with the second part: 1. Kinetic energy is 1. the flow of electrons in one direction. 2. Static electricity is 2. the energy of position. 3. Potential energy is 3. a discharge of electricity. 4. The electric current is 4. the energy of motion. 5. The direct current is 5. the flow of moving electrons. 6. Lightning is 6. electricity at rest. VI. Fill in the blanks with the words from the box: as well, voltage, wires, decreases, terminals, determine, particles, direct current. 1. Atmospheric pressure before thunderstorm. 2. We must the steam pressure in the turbine. 3. A battery is a source of a. 4. What does the atom consist of? 5. There are in the battery. 6. High is dangerous. 7. are made of different metals. 8. Lomonosov knew German, French, Greek and Latin.

4 Grammar. I. Rewrite the given sentences in Passive voice. Frank builds a house. A house is built. or A house is built by Frank. 1) Mr Jones watches the film.. 2) The people speak English.. 3) He reads comics.. 4) We play volleyball.. 5) They sing the song.. 6) I take photos.. 7) She does the housework.. 8) The policemen help the children.. 9) He writes text messages.. 10) Mother waters the flowers. II. Rewrite the given sentences in Passive voice. Passive sentences in the Simple Past. Frank built a house. A house was built. or A house was built by Frank. 1) She bought four apples.. 2) We won the match.. 3) The man stole the blue car.. 4) The police arrested the thieves.. 5) Jack swam the 200 metres.. 6) The dog bit the old lady..

5 7) Tom and Max ate five hamburgers.. 8) Oliver taught the children.. 9) Victoria rode the brown horse.. 10) Grandmother told good stories. III. Rewrite the sentences using Passive voice. (Mixed Tenses) Peter writes a letter. A letter is written. or A letter is written by Peter. 1) Julia rescued three cats.. 2) The students handed in the reports.. 3) Maria crashed into the blue car.. 4) Alex learned the poem.. 5) Steven has forgotten the book.. 6) The mechanic has not repaired the DVD recorder.. 7) They play handball.. 8) Sue puts the rucksack on the floor.. 9) The girls had lost the match.. 10) The teacher is not going to open the window. IV. Rewrite the given sentences in Passive voice. Sometimes there are two possible answers (two objects in the active sentence). Do not use contracted/short forms. Tim gave Lisa some flowers.

6 Some flowers were given to Lisa by Tim. or Lisa was given some flowers by Tim. 1) They don't speak English in this shop.. 2) Kevin asked Dennis a question.. 3) Somebody built the house last year.. 4) She gives him a box.. 5) Max will look after him.. 6) The waiter brought Fred a big steak.. 7) Somebody broke into our bungalow last Friday.. 8) The teacher told us a joke.. 9) They will meet Doris at the station.. 10) Michael has not sent me a text message. V.Put in the correct form of the verb in Passive into the gaps. Use the verb and the tense given in brackets. A letter by Peter. (to write - Simple Present) A letter is written by Peter. 1) The words by the teacher today. (to explain - Simple Present) 2) We a letter the day before yesterday. (to send - Simple Past) 3) This car. It's too old. (not/to steal - will-future) 4) This street because of snow. (already/to close - Present Perfect) 5) A new restaurant next week. (to open - will-future) 6) He to the party yesterday. (to invite - Simple Past) 7) The blue box. (can/not/to see - Simple Present)

7 8) I the book by my friend last Sunday. (to give - Simple Past) 9) The dishes by my little brother. (not/to wash - Present Perfect) 10) I by Robert. (not/to ask - will-future) VI. Decide whether the sentences are written in Active or Passive. They listen to music. She is reading an . These cars are produced in Japan. Alan teaches Geography. German is spoken in Austria. Lots of houses were destroyed by the earthquake. Henry Ford invented the assembly line. The bus driver was hurt. You should open your workbooks. Houses have been built. Boys like to play soccer. This room has been painted blue. Cricket is played in Australia. I am given a book. We have lost our keys. You might see dolphins here. The report must be completed by next Friday. They were singing a song. A letter was written to her. The bike is being repaired.