Vocabulary Exercises. 1.Find the equivalents to the words 1.To repel 2

1. Find the equivalents to the words

1.To repel 2. Propagate 3. stationary charge 4. To attract 5. Aerial 6. strength of field 7. per unit charge 8. uniform field 9. nonuniform field 10. like charges 11. wire 12. transverse 13. variable 14. line of force

a. однородное поле b. притягивать c. антенна d. силовая линия e. поперек f. напряженность поля g. на единицу заряда h. отталкивать i. неоднородное поле j. одноименные заряды k. неподвижный заряд l. провод m. распространять n. переменный

2. Fill in the blanks with a suitable word. Use the correct form:

To repel, to attract, to affect, to increase, to decrease, to depend on, to contain, to vary, to consist of, an excess, a lack.

1. Various factors..... the resistance of a conductor.

2. The resistance of metals …… with a rise in temperature.

3. The resistance of carbon, semiconductors...... as their temperature is raised.

4. How does the resistance of a conductor...... with its length?

5. Objects that are similarly charged... each other; those with unlike charges... each other.

6. All matter....... both positive and negative charges.

7. An ordinary uncharged atom...…the same number of protons and electrons.

8. Resistivity... the material composing the wire and its temperature.

9. The rubber rod becomes negatively charged due to... of electrons and the fur becomes positively charged due to... of electrons.

Part II.

1. Read the texts and make up questions of different types:

Wave types

A wave is a disturbance that propagates through empty space or a medium such as air or water, usually transporting energy as it travels.

In «transverse waves», the disturbance is at right angles to the wave's direction of motion. Electromagnetic radiation, including visible light, is a form of transverse wave in which magnetic and electric fields oscillate at right angles to the wave’s direction of travel. In «longitudinal waves», the disturbance is parallel to the wave's direction. These include sound waves in gases and liquids. Water waves are an example of a wave that is both transverse and longitudinal - a floating cork will move in a circle as a wave washes past it.

Waves are characterized by their wavelength (the distance between peaks or compressions], frequency (the rate at which waves pass a given point and amplitude or intensity. Standing or stationary waves occur when waves are held in a fixed position - for instance, when a guitar string vibrates. Such waves always involve a whole or half-number of waves, and hence the length of the string determines the wavelengths it can maintain.

How Does a Radio Work?

The space around you may look empty—but it isn’t. At all times it is filled with radio frequency waves from nearby radio stations. They are causing minute vibrations in all the metal objects in the room. But you can hear these vibrations only if you turn on your radio. Your radio picks up the radio waves of the station you want to hear and turns them into sound waves. How does it do this?

1. Your radio’s antenna (or aerial wire) picks up all the radio frequency currents that are in the air around it.

2. The tuner selects the frequency of the desired station and blocks out the frequencies of other stations.

3. Now your radio separates the program current from the carrier current. Electronic devices block off the carrier current so that only the program current is left.

4. The program current, which is very weak, must be amplified until it can operate the loudspeaker. This is done by transistors.

5. The loudspeaker changes the program current into sound waves. These sound waves are a copy of those in the broadcasting studio.

2. In pairs ask and answer your questions.

3. Draw a.«longitudinal wave», b.«transverse wave» in your copybooks.

a. …………………………………………………………..

b. …………………………………………………………..

4. Word search

1. What eleven-letter plural noun in the reading means «tiny electronic devices made from semiconductors that control the flow of electrical current»? ___________________________

2. What eight-letter plural noun in the reading means «places with electronic equipment for sending out radio or TV programs»__________________________

3. What five-letter adjective in the reading means «made of a chemical— such as iron, gold, or aluminum—that conducts electricity»? ___________________________

5. Circle a letter to show the antonym of the boldface word in each sentence.

1. Nearby radio stations fill the air around you with radio frequency waves.

a. overlapping b. faraway c. powerful

2. In order to operate the loudspeaker, the program current must be amplified.

a. ignited b. refined c. silenced

3. The tuner selects the frequency of the desired station.

a. best b. unwanted c. chosen

4. The space around you is never empty.

a. quiet b. occupied c. hollow

6. In a different context, the same word can be a different part of speech. Notice how the boldface words from the reading are used in each sentence. Then identify the part of speech by writing noun, verb, or adjective.

1. ____________________ Is that information current or out-of-date?

2. ____________________ Will you take a minute to answer my question?

3. ____________________ Ed programs his computer to do specialized tasks.

4. ____________________ The TV programs I like are on Tuesday night.

5. ____________________ Minute particles of dust covered the furniture.

6. ____________________ The North Atlantic current moves across the ocean from Newfoundland to England.

7. Study definitions, read and translate the examples:

Current - a flow of electric charge or the rate of that flow.

E.g. When the magnet and the wire move near each other, an electric current passes through the wire.

Electricity - a fundamental form of kinetic, or potential, energy created by the movement of charged particles, such as electrons.

E.g. In 1831, a former bookbinder named Michael Faraday proved that a magnetic field could create electricity.

Electromagnet - a core of magnetic material surrounded by a coil of wire through which an electric current is passed to magnetize the core.

E.g. Electromagnets are used in doorbells, loudspeakers, electric motors, and to lift large amounts of magnetic materials, such as scrap iron.

Magnetism - the phenomenon of physical attraction for iron observed in magnets, inseparably associated with moving electricity and characterized by fields of force

E.g. Scientists have figured out how to create magnetism with electricity by running an electric current through loops of wire.

8. Give definitions to the following and use these words in different contexts:

1. Wavelength -

2. Frequency-

3. Amplitude-

4. Entropy -

5. Generator –

9. In your own words explain how telegraph works.

Part III

1. Read the texts, translate and write down unit measures:

Electric charge

Electric charge is a property of many standard model particles, including the electron. This property makes them feel a force from other charged particles. Electrical charge can be either negative or positive, with negatively charged particles attracting positively charged ones while repelling their own kind.

The unit of electric charge is called the coulomb [C]; 1 coulomb is the charge transported per second by an electric current of 1 ampere. The negative charge of an electron is -1.602 x 10~19C. For simplicity, the electron charge is often denoted as -1, while that on a positively charged proton is +1.

Electric charge plays a pivotal role in our very existence, allowing solid structures like the Earth, buildings and animals to exist. Atoms are mostly empty space, but they don't fall through each other due to repulsion between electrons in neighbouring atoms. Charged particles zinging around in the Sun's atmosphere also play a crucial role by generating the radiation that keeps our planet's surface warm and hospitable.

Magnetism

Magnetism is a property of materials that makes them experience a force in a magnetic field. It explains why iron filings line up in ordered patterns near a bar magnet for instance, and why fridge magnets stick to fridges.

Bar magnets are strips of magnetized metal, usually iron, that form a «dipole" field with a north and south pole. Opposite poles attract each other, while like poles repel. The magnetic field of a permanent magnet arises because electrons inside it generate their own tiny magnetic fields due to an intrinsic property called spin, and in materials like iron, the spins of unpaired electrons tend to line up.

Scientists have known since the early 1800s that there is a deep connection between magnetism and electric current. For instance, an electric current flowing through a coil of wire creates a dipole magnetic field similar to that of a bar magnet. Modern electromagnets have achieved record-breaking magnetic fields of 35 teslas, where 1 tesla is about 20,000 times stronger than the Earth's magnetic field.

2. On the lines below, write either the abbreviation or the whole word that matches.

1. __________________ = MHz

2. hertz = __________________

3. __________________ = min.

4. kilohertz = _______________

5. __________________ = oz.

6. __________________ = ft.

7. quart = __________________

3.Continue the list with the units presented in the texts above, explain them.

4.Translate from Russian into English:

1. Использование электрической энергии изменило весь наш образ жизни.

2. Чтобы понимать действие различных электрических машин и приборов, мы должны знать основ­ные законы электричества.

3. Вещества, проводящие электри­чество, называются проводниками.

4. Вещества, не прово­дящие электричество, называются изоляторами.

5. Два по­ложительно заряженных предмета отталкивают друг друга

6. Любой положительно заряженный предмет притягивает любой отрицательно заряженный предмет.

7. Электроскоп представляет собой прибор для обнаружения присутствия электрического заряда.

8. Существует закон, управляющий всеми явлениями природы. Этот закон называется законом сохранения энергии.

9. Существует много различных форм энергии.

10. Существуют кинетическая энергия, тепловая, электрическая, химическая, ядерная и энергия излучения.

Phrasal verbs in academic English

Phrasal verbs often have one-word synonyms. These are usually of Latin origin and sound more formal than their phrasal verb equivalent but both are appropriate when writing or talking about academic subjects. Vary your language by using both.

phrasal verb	synonym	example
put forward (an idea/view/optnion/ theory/plan)	present	In her latest article Kaufmann puts forwarda theory which is likely to prove controversial.
carry out (an experiment / research)	conduct	I intend to carry outa series of experiments.
make up	constitute	Children under die age of 15 make upnearly half of the country's population.
be made up of	consist of	Parliament is made up oftwo houses.
point out	observe	Grenne points outthat the increase in life expectancy has led to some economic problems.
point up	highlight	The study points upthe weaknesses in the current school system.
set out (to do something)	aim	In his article Losanov sets outto prove that...
set out	describe	The document sets outthe terms of die treaty.
go into	discuss	In this book Sergeant goes Intodie causes of the Civil War in some depth.
go/look back over	revise, review	Please go/look back overthis term’s notes.
go through	check	Go throughyour calculations carefully.

5. Rewrite the sentences replacing the underlined word in each sentence with a phrasal verb from the table. Note that both versions of each sentence are equally appropriate.

1 We conducted a series of experiments to test out our hypothesis.

2 Before the test you should revise Chapters 7 and 8 of your textbooks.

3 In his article on the American Civil War Kingston discusses the reasons why the situation developed in the way it did.

4 Cole presents some fascinating theories on the development of language m his latest book.

5 The psychologist observed that it was very unusual for a young child to behave in this way.

6 Please check your work again carefully before handing it in.

7 In this article Simpson aims to prove that the Chinese reached America long before the Vikings.

8 Women now constitute over half the student population in most universities in this country.

6.Match the beginning of each sentence with the most appropriate ending.

1. Feudal society was made   2. Carlson was the first to put   3. Her results appear to go 4. The investigation pointed   5. It took him a long time to work countries. 6. The geography book sets

a. forward a convincing theory with regard to this question. b. up the flaws in the school’s testing methods. c. out the solution to the algebra problem. d. out a lot of basic information about all the world’s countries. e. against what she had found in her earlier studies. f. of dearly defined classes of people.

7. Answer these questions:

1. What sort of things might a scientist carry out?

2. If you want to study something in more depth, what might you go on to do after getting a first degree?

3. What do postgraduate students typically have to write up at the end of their studies?

4. What sort of things do good students regularly look back over?

5. What sorts of things do scholars typically put forward in their lectures or articles?

6. Why is it sensible to go through any maths calculations that you had to make as part of a research study before you draw any conclusions?

Part IV

Grammar

The bare infinitive

We generally use to with the infinitive, e.g. I want to see you. However, in some cases, we use the bare infinitive: that is, the infinitive without to.

USES

After modals and after the auxiliaries do/did:

You must come.

They may arrive soon.

Did you pass the exam?

After Let’s...:

Let’s go out tonight.

After make + noun/pronoun object:

He made me come here.

After would rather:

I’d rather walk there than take the bus.

I’d rather not stay out late tonight.

After had better:

We’d better go home now

After Why not…?

Why not phone me tomorrow?

After a verb of perception+ object:

I didn’t hear you come in.

After the verb help, we can use the to-infinitive or the bare infinitive:

Can you help me (to) open this?

1. In your notebook, copy the dialogue underlining all the infinitives and adding to where it is required.

(Two friends, Alex and Megan, are talking.)

A: Megan, where were you last night? I tried to find you but I couldn’t see you anywhere. James says he didn’t see you come in to the party.

M: Yes Alex, that’s right. I’m sorry. My parents wouldn’t let me come out last night. I wanted see you - honestly I did.

A: Why did your parents make you stay in? They usually allow you go out in the evenings, don’t they?

M: Yes, but I hadn’t finished doing my homework. And they refused let me go out until I had.

A: Oh dear, poor you. Oh well, never mind. Let’s do something tonight instead.

M: OK. Actually, I’d like see that new film.

A: Would you? I suppose it might be quite good but I’d rather just go out to the cafe. I was hoping have a chance talk to you properly.

M: Well, why not do both? We could go to the early showing of the film and then go to the cafe.

A: I’m not sure I can afford go to the cinema.

M: That’s all right. I’ve got some money.

A: So what time would you like meet, then?

M: Six o’clock I suppose - in the cinema. I’ll try get there a bit earlier and buy the tickets.

2. Role play your own dialogue (use the expressions from the dialogue)

3. Put “to” before the infinitive where it is necessary.

1. My son asked me … let him … go to the club.
2. You must make him … practice an hour a day.
3. She was made … repeat the song.
4. He is not sure that it can … be done, but he is willing … try.
5. Let me … help you with your work.
6. She asked me … read the letter carefully and … write an answer.
7. You ought … take care of your health.
8. I looked for the book everywhere but could not … find it.
9. He was seen … leave the house.
10. We had … put on our overcoats because it was cold.
11. The man told me not … walk on the grass.
12. Have you heard him … play the piano?
13. You had better … go there at once.
14. I would rather not … tell them about it.
15. We shall take a taxi so as not … miss the train.

4. Put “to” where necessary.

1. I think you ought … apologize.
2. Make him … speak louder.
3. Help me … carry this bag.
4. My son asked me … let him … go to the theatre.
5. I must … go to the country.
6. It cannot … be done to-day.
7. She asked me … read the letter carefully and … write an answer.
8. The man told me not … walk on the grass.
9. Let me … help you with your work.
10. She ought … take care of her health.
11. We had better … stop to rest a little.
12. I don’t know what … do.
13. He was seen … leave the house.
14. We have come … ask whether there is anything we can … do.
15. We heard the siren … sound and saw the ship … move.
16. I cannot … go there now, I have some work … do.
17. During the crossing the passengers felt the ship … toss.
18. You must make him … practice an hour a day.
19. He is not sure that it can … be done, but he is willing … try.
20. I looked for the book everywhere but could not … find it.
21. He said that she might … come in the evening.
22. She was made … repeat the song.
23. Would you rather … learn shorthand than typewriting?

5. Translate into English using the Objective Infinitive Construction (Complex Object) where possible.

1. Он хочет, чтобы мы пришли к нему сегодня.
2. Я хотел бы, чтобы вы подождали меня здесь.
3. Он хочет, чтобы его сын стал врачом.
4. Он хочет, чтобы его послали в С.-Петербург на конференцию.
5. Она хочет, чтобы ее пригласили на вечер.
6. Мы не хотели, чтобы нас прерывали.
7. Хотите ли вы, чтобы я вам помог?
8. Я хочу, чтобы его статья была опубликована.
9. Доктор не хочет, чтобы вы ехали на юг.
10. Он хочет, чтобы груз был застрахован.
11. Она не любит, чтобы дети готовили уроки вечером.
12. Она любит, чтобы обед был вовремя.
13. Он не любит, когда его прерывают.
14. Он хочет, чтобы ему задавали вопросы.

6. Make infinitives (add “to”) or gerunds (add “-ing”) of the verbs in brackets to make the following sentences grammatically correct.

1. When I’m tired, I enjoy... television. It’s relaxing. (watch)
2. It was a nice day, so we decided... for a walk. (go)
3. It’s a nice day. Does anyone fancy... for a walk? (go)
4. I’m not in a hurry. I don’t mind... (wait)
5. They don’t have much money. They can’t afford... out very often. (go)
6. I wish that dog would stop... It’s driving me mad. (bark)
7. Our neighbour threatened... the police if we didn’t stop the noise. (call)
8. We were hungry, so I suggested... dinner early. (have)
9. Hurry up! I don’t want to risk... the train. (miss)
10. I’m still looking for a job but I hope... something soon. (find)

7. Complete the following sentences with infinitives (add “to”) or gerunds (add “-ing”) of the verbs below to make them grammatically correct.

1. He tried to avoid... my question.
2. Could you please stop... so much noise?
3. I enjoy... to music.
4. I considered... for the job but in the end I decided against it.
5. Have you finished... your hair yet?
6. If you walk into the road without looking, you risk... knocked down.
7. Jim is 65 but he isn’t going to retire yet. He wants to carry on....
8. I don’t mind you... the phone as long as you pay for all your calls.
9. Hello! Fancy... you here! What a surprise!
10. I’ve put off... the letter so many times. I really must do it today.
11. What a stupid thing to do! Can you imagine anybody... so stupid?
12. Sarah gave up... to find a job in this country and decided to go abroad.

8. Make infinitives (with or without “to”) or gerunds (add “-ing”) of the verbs in brackets to make the following sentences grammatically correct.

1. She doesn’t allow... in the house. (smoke)
2. I’ve never been to Iceland but I’d like... there. (go)
3. I’m in a difficult position. What do you advise me...? (do)
4. She said the letter was personal and wouldn’t let me...it. (read)
5. We were kept at the police station for two hours and then we were allowed... (go)
6. Where would you recommend me... for my holidays? (go)
7. I wouldn’t recommend... in that restaurant. The food is awful. (eat)
8. The film was very sad. It made me... (cry)
9. Carol’s parents always encouraged her... hard at school. (study)

Verbs of perception + object + ing or the bare infinitive

Verbs of perception (see, notice, look at, watch, feel, hear, listen to) can be followed by the ing form or the bare infinitive. The verb smell can only be followed by the ing form:

The use of the bare infinitive describes the complete action:

I watched her play tennis. (I saw the whole game.)

The use of the ing form describes the action in progress:

/ watched her playing tennis. (I saw the game in progress.)

The ing form after a verb of perception is a present participle. Verb of perception + present participle is more common than verb of perception + bare infinitive. The difference between the use of the present participle and the use of the bare infinitive is often very small:

I always hear the birds singing in the mornings.

1 always hear the birds sing in the mornings.

Note: We use a few other verbs with the present participle: find, discover, catch, leave, keep. These verbs cannot be followed by the bare infinitive:

I found her looking in my desk.

9.Rewrite the following pairs of sentences as one sentence, using the -ing form or a bare infinitive.

Model: I saw you the other day. You were cycling to work. I saw you cycling to work the other day. I heard him early this morning. He left the house. I heard him leave the house early this morning.

1. She stood there and watched him. He drove away.

2. Did you notice me? I was crying

3. I’ve often seen you. You’ve been walking along the beach with your dog.

4. Have you ever heard him? He plays the saxophone.

5. I expect to find you when I get back. You’ll be working hard.

6. Did you hear me? I arrived.

7. I looked at the child and felt very sad. She was smiling up at me.

8. We heard them. They were arguing all night.

9. I can feel my hands. They are shaking.

10. I watched you and then I left. You went to sleep.

11. I can smell smoke. It’s coming in through the windows.

12. He watches me every weekend. I play football.

10. Analyze the following sentences:

1. A compass needle brought close to a long straight iso­lated wire carrying an electric current will tend to align itself at right angles to the plane passing through the axis of the wire and the pivot of the needle. 2. When making theoretical calculations we can, however, imagine a unit charge to be used provided we do not take into account any modification of the field which its presence might cause. 3. Thus we define the amount by which the potential at a given point R exceeds that at another point P as the net amount of work which must be done against the electric force acting on it in order to take a unit positive charge from P to R, it being supposed that the presence of the unit charge does not modify the field.

Part V

Listening

Use of electricity to cure mental diseases

1. Listen to the talk about the use of electricity to cure mental diseases, decide whether the statement is true or false.

1. Parkinson's disease causes uncontrollable shaking, or tremors

2. Mr. Dewsnap couldn't use... the right side of his body.

3. Caleb Kemere has been using brain stimulation in his experiments on frogs.

4. A brain chemical called Dopamine helps control movement.

5. Researchers need to settle some small problems such as what electrical device to use.

2. Listen again and take notes.

3. Describe this method and its difficulties in your own words (in pairs)

Writing (Rendering of the text)

1. Read the text and define the main idea.

2. Make outline and summary of the text.

3. Think about your own ideas on the topic (make use of listening task).

4. Render the text in writing (follow the plan and use expressions – see Appendix)

Feeling electric fields

Why is electricity dangerous to humans? The main reason is that the human body is controlled by ‘electric wires’ itself. As a result, electricity applied to human bodies from the outside interferes with the internal signals. This has been known since 1789. In that year the Italian medical doctor Luigi Galvani (1737–1798) discovered that electrical current makes the muscles of a dead animal contract. The famous first experiment used frog legs: when electricity was applied to them, they twitched violently. Subsequent investigations confirmed that all nerves make use of electrical signals. Using electricity, one can make fresh corpses move, for example. Nerves are the «control wires» of animals. We will explore nerves in more detail below.

Being electrically controlled, all mammals can sense strong electric fields. Humans сan sense fields as low as10kV /m, when hair stands on end. In contrast, several animals can sense much weaker electric (and magnetic) fields. Sharks, for example, can detect fields down to 0.5 μV/m using special sensors, the Ampullae of Lorenzini, which are found around their mouth. Sharks use them to detect the field created by prey moving in water; this allows them to catch their prey even in the dark. The elephantnose fish (Gnathonemus petersii), the salamander and the platypus (Ornithorhyncus anatinus), the famous duck-billed mammal, can also sense electric fields, but achieve only sensitivities of the order of mV/m. Like sharks, they use this ability to detect prey in water which is too muddy to see through. The muscles in living prey generate electric fields. This method is also used by the elephantnose fish. The achieved sensitivity is below 2 mV /m. Certain fish, the so-called weakly-electric fish,even generate a weak field in order to achieve better prey detection. In fact, several electric fish use time-varying electric dipole fields to communicate! They tell each other their species, their sex, their identity, and communicate about courtship, aggression, appeasement and dangers. The frequencies they use are in the range between a few and 200 Hz, and the fields are dipole fields created between the anterior and posterior sections of their bodies.

No land animal has special sensors for electric fields, because any electric field in air is strongly damped when it encounters a water-filled animal body. Indeed, the usual atmosphere has a low, vertical electric field of around 100 V/m; inside the human body this field is damped to the μV/m range, which is far less than an animal’s internal electric fields. In other words, humans do not have sensors for low electric fields because they are land animals. (Do humans have the ability to sense electric fields in water? Nobody seems to know.) However, there a few exceptions. You might know that some older people can sense approaching thunderstorms in their joints. This is due the coincidence between the electromagnetic field frequency emitted by thunderclouds – around 100 kHz – and the resonant frequency of nerve cell membranes.

The water content of the human body also means that the electric fields in air that are found in nature are rarely dangerous to humans. But whenever humans consciously sense electric fields, such as when high voltage makes their hair stand on end, the situation is potentially dangerous.

The high impedance of air also means that, in the case of time-varying electromagnetic fields, humans are much more prone to be affected by the magnetic component than by the electric component

Can humans feel magnetic fields? So far, there is no definite answer. Magnetic material seems to be present in the human brain, but whether humans can feel magnetic fields is still an open issue. Maybe you can devise a way to check this?

(from Christoph Schiller “MOTION MOUNTAIN”)

Part VI

Listening 2

Lightning and electricity

1. Listen and choose the best answer

1. Benjamin Franklin was…

a. Politician

b. Scientist and inventor

c. All of the above

2. Franklin’s experiment would discover…

a. If lightning would pass through kite

b. If lightning would pass through metal

c. If lightning would strike a tree

3. The kite in the experiment was made….

a. From light metal

b. From brightly colored paper

c. From light cloth

4. The experiment took place in….

a. June, 1752

b. July, 1762

c. January, 1742

5. The experiment proved that lightning is…

a. Sound

b. Light

c. Electricity

6. Fulgurites form when…

a. Lightning strikes sand

b. Lightning strikes rock

c. All of the above

7. Franklin’s invention is…

a. Electricity

b. Metal kite

c. None of the above

2. Explain Franklin’s experiment and its effect

3.Translate from Russian into English

Молния — гигантский электрический искровой разряд в атмосфере, обычно может происходить во время грозы, проявляющийся яркой вспышкой света и сопровождающим её громом. Молнии также были зафиксированы на Венере, Юпитере, Сатурне и Уране и др. Ток в разряде молнии достигает 10—300 тысяч ампер, напряжение — от десятков миллионов до миллиарда вольт. Мощность разряда - от 1 до 1000 ГВт.

Электрическая природа молнии была раскрыта в исследованиях американского физика Б. Франклина, по идее которого был проведён опыт по извлечению электричества из грозового облака. Широко известен опыт Франклина по выяснению электрической природы молнии. В 1750 году им опубликована работа, в которой описан эксперимент с использованием воздушного змея, запущенного в грозу. Опыт Франклина был описан в работе Джозефа Пристли.

Средняя длина молнии 2,5 км, некоторые разряды простираются в атмосфере на расстояние до 20 км.

Удары М. могут сопровождаться разрушениями, вызванными её термическими и электродинамическими воздействиями, а также некоторыми опасными последствиями, возникающими в результате её электромагнитного и светового излучения. Наибольшие разрушения вызывают удары М. в наземные объекты при отсутствии хороших токопроводящих путей между местом удара и землёй. От электрического пробоя в материале образуются узкие каналы, в которые устремляется ток М. Поскольку в каналах создаётся очень высокая температура, часть материала интенсивно испаряется со взрывом. Это приводит к разрыву или расщеплению объекта, пораженного М., и воспламенению его горючих элементов. Наряду с этим возможно возникновение больших разностей потенциалов и электрических разрядов между отдельными предметами внутри строения. Такие разряды могут также явиться причиной пожаров и поражения людей электрическим током.

Speaking

1.Deliver a lecture on Electric current, give all necessary definitions and explain formulas. Use the plan (you may add some points):

1. What is called an electric current?

2. What is resistance?

3. What factors affect electrical resistance?

4. What is resistivity?

5. How can the resistance of a conductor be determined if its length, material and cross-section are known?

6. Define effects.

2. Discussion. Work in pairs or small groups. Compare your answers.

For fun

1. Birds come to no harm when they sit on unprotected electricity lines. Nevertheless, one almost never observes any birds on tall, high voltage lines of 100 kV or more, which transport power across longer distances. Why?

2. Why do we often see shadows of houses and shadows of trees, but never shadows of the electrical cables hanging over streets?

3. A pure magnetic field cannot be transformed into a pure electric field by change of observation frame. The best that can be achieved is a state similar to an equal mixture of magnetic and electric fields. Can you provide an argument elucidating this relation?

4. Five positive charges of magnitude q are arranged symmetrically around the circumference of a circle of radius r. What is the magnitude of the electric field at the center of the circle? (k =1/4πϵ0)

(A) 0

(B) kq/ r²

(C) 5 kq/ r²

(D) (kq/ r²) cos (2π/ 5)

(E) (5 kq/ r²) cos (2π/ 5)

5. A 3-microfarad capacitor is connected in series with a 6-microfarad capacitor. When a 300-volt potential difference is applied across this combination, the total energy stored in the two capacitors is

(A) 0.09 J

(B) 0.18 J

(C) 0.27 J

(D) 0.41 J

(E) 0.81 J

Supplementary reading

Дата добавления: 2015-10-23