2_kurs_4_semestr

UNIT 12

Voltage

Read the text and express its main idea.

What exactly is voltage? If you ask an engineer, he will probably tell you that voltage drives electric current. And so it does – but what is it? What is its nature? ‗Some sort of energy‘, you might expect. And so it is, although the technical answer is that voltage is electric potential energy per unit charge. Voltage, also called electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field. The greater the voltage, the greater the flow of electrical current through a conducting

or semiconducting medium for a given resistance to the flow. Voltage is symbolized by an uppercase italic letter V or E. The standard unit is the volt, symbolized by a non-italic uppercase letter V. One volt is equal to one joule per coulomb.

Since voltage is defined as energy per unit charge, it should be obvious that the product of voltage and charge is energy (or work) i.e. W = qV. Thus if a charge of 1 Coulomb is moved through a potential difference of 1volt, 1 joule of work is done.

Voltage can be direct or alternating. A direct voltage maintains the same polarity at all times. In an alternating voltage, the polarity reverses direction periodically. The number of complete cycles per second is the frequency, which is measured in hertz (one cycle per second), kilohertz,

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megahertz, gigahertz, or terahertz. An example of direct voltage is the potential difference between the terminals of an electrochemical cell. Alternating voltage exists between the terminals of a common utility outlet.

A voltage produces an electrostatic field, even if no charge carriers move (that is, no current flows). As the voltage increases between two points separated by a specific distance, the electrostatic field becomes more intense. As the separation increases between two points having a given voltage with respect to each other, the electrostatic flux density diminishes in the region between them.

Give synonyms for the following words: quantitative, to conduct, to increase, separation, distance.

Criticize the following statements:

―He touched the wire, and 10000 volts went through him.‖ ―That battery has a charge of 9 volts.‖

―You used up the charge of the battery.‖

Discussion Question.

I once touched a piece of physics apparatus that had been wired incorrectly, and got a several-thousand-volt voltage difference across my hand. I was not injured. For what possible reason would the shock have had insufficient power to hurt me?

Make a plan and try to retell the text using your plan.

Present a report on Alessandro Volta‟s life and work.

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GRAMMAR

Shall / Will

 We use shall in questions

a) when we offer to do something.

e.g. Shall I carry your shopping for you? (Would you like me to carry

your shopping for you?)?

b) when we make suggestions.

e.g. Shall we visit your cousins tonight?

c) When we ask for suggestions.

e.g. ‗What time shall I call you?‘ ‗Give me a call at six.‘

We use will in questions when we want to make a request. e.g. Will you phone the doctor, please?

Ствердження/заперечення

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EXERCISES

1. Fill in shall or will.

1.…Shall…I help you with the washing-up?

2.…we have pizza for dinner tonight?

3.…you carry this for me, please?

4.What …we buy for Bob‘s birthday?

5.…you answer the phone, please?

6.Where …we sit in the classroom?

7.…you take the rubbish out for me, please?

8.…we have a barbecue next weekend?

2. Fill in the gaps with the question words from the list and shall we.

1.‗Where shall we go on Saturday night?‘ ‗Let‘s go to a restaurant.‘

2.‗…spend on a present for Jane?‘ ‗$50.‘

3.‗…pay?‘ ‗In cash.‘

4.‗…invite to the party?‘ ‗Just our friends.‘

5.‗…decorate the house?‘ ‗This weekend.‘

6.‗…do on your birthday?‘ ‗We can have a party.‘

7.‗… do on Monday?‘ ‗Why don‘t we go swimming?‘

8.‗…take the dog for a walk?‘ ‗Let‘s take him to the beach.‘

3. Mrs. Patterson asks the nanny to do some things while she‟s gone. Use prompts to make requests, as in the example.

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UNIT 13

Resistance

Read the text and be ready to discuss the topic.

The electrical resistance of a wire or circuit is a way of measuring the resistance to the flow of an electrical current. A good

electrical conductor, such as a copper wire, will have a very low resistance. Good insulators, such as rubber or glass insulators, have a very high resistance. The resistance is measured in ohms, and is related to the current in the circuit and voltage across the circuit by

Ohm‘s law. According to Ohm‘s law, a circuit‘s

resistance is equal to its voltage divided by the amount of current. For a given voltage, a wire with a lower resistance will have a higher current.

The resistance of a given piece of wire depends of three factors: the length of the wire, the cross-sectional area of the wire, and the resistivity of the material composing the wire. To understand how this works, think of water flowing through a hose. The amount of water flowing through the hose is analogous to the current in the wire. Just as more water can pass through a fat fire hose than a skinny garden hose, a fat wire can carry more current than a skinny wire. For a wire – the larger the cross-sectional area, the lower the resistance; the smaller the cross-sectional area, the higher the resistance. Now consider the length. It is harder for water to flow through a very long hose simply because it has to travel farther. Analogously, it is harder for current to travel through a longer wire. A longer wire will have a greater resistance. The resistivity is a property of the material in the wire that depends on the chemical composition of the material but not on the amount of material or the shape

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(length, cross-sectional area) of the material. Copper has a low resistivity, but the resistance of a given copper wire depends on the length and area of that wire. Replacing a copper wire with a wire of the same length and area but a higher resistivity will produce a higher resistance. In the hose analogy, it is like filling the hose with sand. Less water will flow through the hose filled with sand than through an identical unobstructed hose. The sand in effect has a higher resistivity to water flow. The total resistance of a wire is then the resistivity of the material composing the wire times the length of the wire, divided by the cross-sectional area of the wire.

Why is this sign a joke?

Explain what the term „resistance‟ means in your own words.

Lightning is a natural, electrical phenomenon. It is caused by the

accumulation of a large electrical charge over time resulting from air,

dust, and water droplets transporting small electrical charges.

Explain how the terms voltage, current, and resistance relate to the process of lightning. In other words, use these three terms to explain the cycle of charge accumulation and lightning discharge.

Does this switch (in the closed state) have a low resistance or a high resistance between its terminals?

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GRAMMAR

Modal Verbs. Revision.

EXERCISES

1. Correct the mistakes.

1.You can go out until you finish eating.

2.Dad, must I borrow the car, please?

3.I haven‘t be able to write the letter yet.

4.He can‘t run long distances when he was a boy.

5.You mustn‘t wake up early tomorrow. It‘s a holiday.

6.He drives a Porsche. He must be poor.

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3. Underline the correct item.

Dear Henry,

I‘m writing to you because I need some advice. 1) Can/Shall you help me, please? My boss offered me a job in Italy and I 2) could/must make a decision about it soon. I‘ve been thinking about it since last week but I 3) haven’t been able to/wasn’t able to decide! I‘m a bit worried that I 4) shall/may not enjoy living in another country. I 5) might/ought to find it difficult to learn Italian. However, I 6) won’t have to/mustn’t stay there if I don‘t like it. What do you think? 7) Should/Will I move to Italy or 8) could/should I stay here? 9)

Could/May you write to me and tell me what you think?

I hope to hear from you soon.

Best wishes,

Ronnie

4. Correct the mistakes.

1.Might we visit Mary and Tony tonight?

2.I‘m not sure where Ed is. He mustn‘t be at work.

3.Will I help you wash the dishes?

4.Martha had a bad cold but she could do all her work at the office.

5.You shouldn‘t go to the dentist if you have toothache.

6.Shall I borrow your pen, please?

7.I might climb trees when I was young.

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UNIT 13

Home-reading

Nikola Tesla

Tesla was born at midnight on July 10th 1856 in the small village of Smiljan, which is in the Lika province of what is now

Croatia. His father was a reverend minister and his mother was known for her inventiveness. The family moved to the nearby city of Gospic in 1862, where Nikola attended school, and then continued his education at Karlstadt in Croatia. In his childhood he had a very inquisitive nature and a practical mechanical sense which earned him respect.

In 1875 he enrolled to study Electrical Engineering at the Austrian Polytechnic School in Graz. After financial struggles prevented him from completing the course, he moved to Budapest, Hungary, in 1881 and worked as a draftsman in the Central Telegraph Office. His skills in electrical matters were soon recognised, and he was placed in charge of the new telephone exchange.

About this time he experienced a visualisation of the invention which would soon make him known all over the world, the Polyphase Alternating Current motor, which used a rotating magnetic field and had no commutator. In 1882 he moved to Paris to take a job with the Continental Edison Company as a junior engineer. In his spare time, he constructed AC motors and dynamos and developed the idea.

In the summer of 1884 he decided to migrate to the United States of America, with the offer of a job to work for Thomas Edison in New York. Tesla worked hard and impressed Edison, but resigned after less than a year over the

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non-payment of a bonus which Tesla expected. Edison also was a strong proponent of the Direct Current system, which Tesla did not agree with.

In his new laboratory in 1887 he had the opportunity to completely develop his Alternating Current Polyphase system, which eventually revolutionised industrial and domestic electric generation, distribution and consumption. Useful motors had already been developed to use Direct Current, but they were less efficient, and the distribution of DC electricity on an industrial scale was impractical, despite the strong (and sometimes underhand) effort which Edison was making.

Tesla was granted 40 patents for his AC system, which were purchased along with generous royalties by George Westinghouse, the industrial giant, and a supporter of the AC system. He worked for Westinghouse for a short time and became a US citizen in 1891. The first crowning glory for Tesla was the 1895 completion of the 50,000 horse-power hydro generating plant at Niagara Falls by Westinghouse.

In his own laboratory in New York, he became interested in higher frequencies, constructing special dynamos, and developing the high frequency oscillator which bears his name, the "Tesla Coil". The currents produced by this device could be used to transmit energy using only one wire, or without wires at all.

High voltage and high frequency work continued. By 1898 he had developed "teleautomatonics", or remote-control, to such an extent that his radio operated boat caused a sensation wherever it was demonstrated.

Tesla developed sensitive wireless receivers and built a large transmitter which generated 12,000,000 volts and an antenna base current of 1,200 amperes, a remarkable achievement for the time. The prime objective was to develop his system of the wireless transmission of power. His dream was to

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