Студопедия
Случайная страница | ТОМ-1 | ТОМ-2 | ТОМ-3
АвтомобилиАстрономияБиологияГеографияДом и садДругие языкиДругоеИнформатика
ИсторияКультураЛитератураЛогикаМатематикаМедицинаМеталлургияМеханика
ОбразованиеОхрана трудаПедагогикаПолитикаПравоПсихологияРелигияРиторика
СоциологияСпортСтроительствоТехнологияТуризмФизикаФилософияФинансы
ХимияЧерчениеЭкологияЭкономикаЭлектроника

Put the verb in brackets into the correct form, Present Continuous or Present Simple.

Читайте также:
  1. A Graphical User Interface (GUI) makes computers easier to use. A GUI uses icons. Icons are pictures which represent programs, folders, and files.
  2. A Present continuous
  3. A Read the text again and choose the correct ending to each sentence.
  4. A) Present Passive quiz
  5. A- Correct the underlined words
  6. A. Put the verbs in brackets into the correct tense.
  7. A. Write sentence or questions with the present perfect.

1. This scientist (to be) never satisfied. He always (to complain).

2. In a vacuum-tube triode there (to be) three electrodes: a cathode, a plate and a grid.

3. When heated the cathode (to emit) electrons.

4. I see in Fig.1 that the electrons (to flow) from the cathode to the plate.

5. The grid (to control) the flow of electrons when the device is switched on.

6. The closer the grid (to be) to the cathode, the more influence it has on the electron flow.

7. Look! The plate current (to decrease).

8. We are decreasing the negative voltage on the grid to 8 volts, and the current gradually (to increase).

9. Due to this property of a triode, it (can) be usedfor amplification.

10. Usually he (to work) as a software maker, but he (to read) lectures now.

11. The number of electrons (to increase) very rapidly in this device.

12. It (to get) late. Let’s finish the experiment.

13. The grid (to be) placed between the cathode and the plate.

14. A: You (to work) hard today. B: Yes, I have a lot to do.

15. Even if a small negative voltage is applied to the grid, this (to result) in a large plate current.

Formulate the rules.

7. Form nouns from the following verbs using the suffix -or, -еrand translate them:

For example:

amplify — усиливать; amplifier — усилитель

 

conduct — проводить (ток);

control — управлять;

detect — обнаруживать, определять;

divide — делить;

learn — учить;

operate — приводить в действие;

heat — нагревать;

insulate — изолировать;

emit — испускать;

direct — направлять;

use — использовать;

rectify — выпрямлять (ток).

 

8. Choose the appropriate English equivalents:

ближе— 1. close; 2. closer; 3.the closest

лучше— 1. good; 2. better; 3. the best

больше— 1. the most; 2. more; 3. much

самый маленький— 1.small; 2. smaller; 3. the smallest

самый большой— 1. the largest; 2. large; 3. larger

выше—1. high; 2. higher; 3. the highest

Remember the spelling: big – bigger

9. Translate the following sentences. Mind the meaning of the highlighted words.

1. The farther the grid is from the cathode, the more the plate current is. 2. The wider the distance between the grid wires, the more the plate current is. 3. The higher the temperature, the lower the conductivity of a metallic conductor. 4. The lower the temperature, the better the conductivity of a metallic conductor. 5. The slower the electrons move, the easier it is to stop them and return them to the space charge. 6. The closer the grid is to the cathode, the more control it will have on electron flow to the plate. 7. The more heavily the material is doped, the lower its electrical resistance will be. 8. The hotter the cathode becomes, the more electrons it emits per unit time (в единицу времени). 9. As the electrons move out into space, they form a cloud (облако) of negative charges. The larger this cloud becomes, the more opposition it offers to additional electrons leaving the cathode. 10. The more negative the grid, the less the plate current will be. 11. The greater the load resistance of a tube amplifier, the greater is the voltage amplification.

 

10. Translate

A. start from the first component

anode current, electron tube, large plate current, semicoductor device, small negative voltage, large negative voltage, gas-filled envelope

B. start from the second component

electron flow, current flow, potential increase

 

11. Translate the following sentences. Start your translation from an adverbial modifier of place.

1. There is one grid in a triode. 2. There are two grids in a tetrode. 3. There are three grids in a pentode. 4. There is no grid in a diode.

Match the following sentences with their translations.

1. The third element is called "a grid". 2. It is placed between the cathode and the plate. 3. The purpose of a grid is to control the flow of electrons. 4. The closer the grid is to the cathode, the more influence it has on the electron flow. 5. The more negative the grid, the less the plate current. 6. A small negative voltage is applied to the grid. 7. This results in a large plate current. 8. Vacuum triodes can amplify current. a. Чем ближе сетка к катоду, тем больше у нее влияние на поток электронов. b. К сетке приложено низкое отрицательное напряжение. c. Это приводит к возникновению большого анодного тока. d. Вакуумные триоды могут усиливать ток. e. Третий элемент называется «сеткой». f. Она помещается между катодом и анодом. g. Назначение сетки – управлять потоком электронов. h. Чем более отрицательна сетка, тем меньше будет анодный ток.

Choose as many words from the table оf ex. 1 as you can and form sensible sentences in Present Continuous (affirmative, negative and interrogative).



For example: In Fig. A the grid is controlling the current flow.

SPECIALIST READING

14. Read the text “Triodes” and choose its best summary.

1. The electron flow in a triode.

2. The influence of the grid on the electron flow.

3. The structure of a triode, basic principles of its operation and functions.

 

In a vacuum-tube triode there are three electrodes: a cathode, a plate and a grid. When heated the cathode emits electrons. Electrons flow from the cathode to the plate. The grid is placed between the cathode and the plate. It controls the flow of electrons. The closer the grid is to the cathode, the more influence it has on the electron flow. Even if a small negative voltage is applied to the grid, this results in a large plate current. If a large negative voltage is applied to the grid, the plate current decreases. For example, the plate voltage is 150 volts. A small negative voltage of 10 volts is applied to the grid. This results in a current flow of 20 m. a. But if the negative voltage on the grid is decreased to 8 volts, this will result in a current of 30 m.a. Due to this property of a triode, it can be used for amplification.

 

15. Read the text again and complete the sentences.

1. In a vacuum-tube triode there are…

2. When heated…

3. Electrons flow…

4. The grid is placed…

5. the flow of electrons.

6. The closer the grid is to the cathode …

Загрузка...

7. … this results in a large plate current.

8. If a large negative voltage is applied to the grid …

9. … it can be used for amplification.

Match the terms in Table A with their definitions in Table B

Table A Table B
1. cathode 2. triode 3. amplification 4. electrode 5. plate a. A vacuum tube having three electrodes or a semiconductor rectifier having three connections. b. The negatively charged electrode by which electrons enter an electrical device. The opposite of anode. c. The positively charged electrode by which the electrons leave a device. The opposite of cathode. d. An increase in strength or intensity, especially of sound. e. A conductor through which electricity enters or leaves an object, substance, or region.

SPEAKING

Work in pairs. Draw a circuit of a triode and ask your partner some questions based on it. Make sure all the questions and answers are in Present Continuous.

For example:

Student A – In what direction are the electrons shown in the scheme moving?

Student B – They are moving towards the plate.

 

17. Summarize the text “Triodes” in 150 words using the following plan:

1. The structure ofa vacuum-tube triode.

2. The principles of its work.

3. The function of a grid.

4. The influence of the distance between the cathode and the grid on the electron flow.

5. The influence of the voltage on the current flow.

6. The grid application.

18. Compare a vacuum-tube triode with a diode using appropriate degrees of comparison and the following words of comparison and contrast: both, like, whereas, unlike, but, however.

For example: 1. When heated in both tubes cathodes emit electrons.

2. A triode can be used for amplification unlike a diode which is used as …

 

Act as an interpreter. Translate the description of the operation of a semiconductor triode given by your group mates from Russian into English.

20. Divide into 2 groups. Group 1 translates Extract A and group 2 – extract B of the text “Heat Transfer and Appearance of Tubes” with a dictionary in writing.

Highlighted words are international. Try to guess their meaning without a dictionary.

Extract A

Any types of vacuum tubes can be recognized from their appearance. A considerable amount of heat is produced when tubes operate. In most circuits the tube is about 30-60% efficient depending on the class of operation (classes A, B, or C), which means that 40-70 % of input power is lost as heat. The requirements for heat removal significantly change the appearance of high-power vacuum tubes.

Most tubes contain two sources of heat when operating. The first one is the filament or heater. Some types contain a directly heated cathode. This is a filament similar to an incandescent electric lamp and some types glow brightly like a lamp, but most glow dimly. (The "bright emitter" type possesses a tungsten filament alloyed with 1-3 % thorium which reduces the work function of the metal, giving it the ability to emit sufficient number of electrons at about 2000 degrees Celsius. The "dull emitter" types also possess a tungsten filament but it is coated by a mixture of calcium, strontium and barium oxides, which emit electrons easily at much lower temperatures due to a monolayer of mixed alkali earth metals coating the tungsten when the cathode is heated to about 800-1000 degrees Celsius.)

The second form of cathode is the indirectly heated form which usually consists of a nickel tube, coated on the outside with the same strontium, calcium, barium oxide mix used in the "dull emitter" directly heated types, and fitted with a tungsten filament inside the tube to heat it. This tungsten filament is usually uncoiled and coated by a layer of alumina, (aluminium oxide), to insulate it from the nickel tube of the actual cathode. This form of construction allows for a much greater electron emitting area and, because the heater is insulated from the cathode, the cathode can be positioned in a circuit at up to 150 volts more positive than the heater or 50 volts more negative than the heater for most common types. It also allows all the heaters to be simply wired in series or paralleled rather than some requiring special isolated power supplies such as specially insulated windings on power transformers or separate batteries.

Extract B

For small-signal tubes such as used in radio receivers, heaters are rated from 50 mW to 5 watts, (directly heated), and about 500 mW to 8 watts for indirectly heated types. Once filament/heater power is included in total power consumption, small tubes have very poor efficiencies. A 6BM8/ECL82 audio stage consumes a total power of some 15 watts for 3.5 watts of useful audio power, giving an efficiency of around 23%. Some signal amplifiers, particularly high-frequency amplifiers such as the 6BA6, consume some 5.9 watts of power in normal operation and deliver only 1.1 watts of power at the plate.

The second source of heat is generated at the anode, when electrons, accelerated by the voltage applied to the anode, strike the anode and impart a considerable fraction of their energy to it, raising its temperature. In tubes used in power amplifying or transmitting circuits, this source of heat will exceed the power dissipated in the cathode heater. (The plates or anodes of 6L6 devices used in guitar amplifiers can sometimes be seen to reach red heat if the bias is set too high, they should not emit any visible radiation when driven at maximum ratings.) No tubes in domestic, music, or studio equipment should operate with glowing anodes.

This heat usually escapes the device by (black body) radiation from the anode/plate as infra red light. Some is conducted away through the connecting wires going to the base but none is convected in most types of tube because of the vacuum and the absence of any gas inside the bulb to convect.

For devices required to radiate more than 500 mW or so, usually indirectly heated cathode types, the anode or plate is often treated to make its surface less shiny, (see black body radiator), and to make it darker, either gray or black. This helps it radiate the generated heat and maintain the anode or plate at a temperature significantly lower than the cathode, a requirement for proper operation.

Other internal elements of high-power tubes, such as control grids and screen grids, may also dissipate heat if carrying large currents. Limits to grid dissipation are listed for such devices to prevent distortion and failure of the grids.

 

In Russian write a content-based summary of the text you have translated.

22. Translate into English the summary made in ex.21 of the text you haven’t read.

Make a reverse written translation (from Russian into English) of the Extract you have translated.

Serve as simultaneous interpreter. Make an oral reverse interpretation of the text.

Find more information about vacuum tubes and tell your group mates.

UNIT III

CONDUCTIVITY

Language Work

Present Simple Passive

am/is/are + done/attracted (past participle)

Active: We call such materials conductors.

Passive: Such materials are called conductors.

They are not called insulators.

When is a negative voltage appliedto the plate?

Present Continuous Passive

am/is/are being + done/considered(past participle)

Active: Look! The student is placing the grid between the cathode and anode.

Passive: Look! The grid is being placed between the cathode and anode by the student.

This figure shows that a voltage is not being applied to the grid at the moment.

Is the circuit being completed while providing the experiment?

Reading

  [t] placed, developed
-ed [d] used, described
  [Id] heated, translated

Forms of the Personal Pronouns and One

Subjective Case (кто?) Objective Case (кому?) Possessive Adjective (чей?) Possessive Pronoun Reflexive Pronoun
I me my mine myself
you you your yours yourself
he him his his himself
she her her hers herself
it it its its itself
we us our ours ourselves
you you your yours yourselves
they them their theirs themselves
one one one’s   oneself

1. Fill in the table.

Noun Verb Adjective Adverb Translation Transcription
ability          
  base     основывать [beis]
consideration   consider       рассмотрение рассматривать  
germanium       германий  
limit   limit     предел ограничивать [′limit]
motion          
particle       частица  
property       свойство  
silicon       кремний  

2. Read and translate the following international words:

Nouns (n): aluminium, atom, computer, dielectric, discussion, generator, germanium, industry, kilowatt, machine, robot, rotor, selenium, steel, structure, temperature, test, turbo-generator.

Adjectives (adj): cryogenic, monolythic, proportional.

Verbs (v): circulate, class, classify, discuss, generate, test.

 

3. Choose the appropriate English equivalents. What do all of them have in common?

притяжение – 1. attraction; 2. attractive; 3. attracted

описание – 1. describe; 2. description; 3. described

нагревание – 1. heater; 2. heating; 3. heat

работа – 1. operator; 2. operate; 3. operation

определение – 1. defined; 2. define; 3. definition

проводник – 1. conductor; 2. conductivity; 3. conducted

направление – 1. direct; 2. direction; 3. directly

выпрямление – 1. rectifier; 2. rectified; 3. rectification

изоляция – 1. insulator; 2. insulated; 3. insulation

эмиссия 1. emission; 2. emit; 3. emitted

 

4. Form adverbs from the following adjectives using the suffix -and translate them:

For example:absolute — абсолютный; absolutely — абсолютно

 

comparative — сравнительный;

direct — прямой;

easy — легкий;

normal — нормальный;

practical — практический;

relative — относительный;

usual — обычный.

 

5. Form adjectives from the following nouns using the suffix -1ess and translate them:

For example:motion — движение; motionless — неподвижный.

 

limit — предел;

wire — проволока;

use — польза;

form — форма;

water — вода;

power — сила, энергия;

time — время.

What’s the meaning of this suffix?

 

6. Translate starting from the first component:

1. atomic cardinal isotopic maximum number natural negative positive 4. absolute elliptical harmonic molecular motion planetary sinusoidal thermal
2. electrostatic static negative charge electrical positive 5. fundamental cathode charged particle elementary resonance
3. critical lower limit upper   6. cotton heat insulation silicon hydrothermal

7. Read the following. Why are these verbs divided into three groups?

A B C
used described compared called decreased developed increased placed switched attracted depended heated translated

8. Give the three forms of the following irregular verbs.

For example: know – knew – known

be – …; have – …; give – … ; show – …; see – …; take – …

Find more in a dictionary and learn them.

 

9. Choose the appropriate English equivalents:

известный —1. knew; 2. known; 3. know

показанный—1. show; 2. showed; 3. shown

увиденный— 1. see; 2. seen; 3. saw

помещенный — 1. place; 2. placing; 3. placed

изолированный— 1. insulate; 2. insulated; 3. insulating

данный — 1. give; 2. given; З. gave

взятый— 1. take; 2. took; 3. taken

названный — 1. called; 2. calling; 3. call

использованный — 1. using; 2. use; 3. used

 

10. Choose the appropriate Russian equivalents to Participles II:

A.1. compared; 2. defined; 3. shown; 4. obtained; 5. decreased; 6. described; 7. called

1. показанный; 2. полученный; 3. описанный; 4. сравниваемый; 5. названный; 6.уменьшенный; 7. определенный

B.1. increased; 2. placed; 3. taken; 4. known; 5. amplified; 6. given; 7. switched on

1. помещенный; 2. известный; 3. данный; 4. включенный; 5. увеличенный; 6. усиленный; 7. взятый

 

11. Do not translate! Define where the subject is the doer of the action.

1. a) The grid controls the flow of electrons. – b) The grid is placed between the cathode and anode.

2. a) A large negative voltage is applied to the grid. – b) We do not apply a large positive voltage to the grid.

3. a) Transistors are used in this function. – b) We use transistors for amplification.

4. a) New devices are being installed here at the moment. – b) They are installing new devices here now.

5. a) The charged particles inside the material can be set in motion. - b) We can set the charged particles inside the material in motion.

6. a) Physicists classify materials according to their electrical properties. – b) Materials can be classified according to their electrical properties.

7. a) Classification is based on the ability of a material to conduct electricity. - b) We base our classification on the number of charged particles.

8. a) Metals, for example, having many free electrons, can readily conduct current at room temperature. – b) Look at this device! Current is being conducted.

How does the use of the Passive Voice depend on the doer of the action?

Translate paying attention to the Passive Voice.

1. Materials can be classified according to their electrical properties. 2. This method is based on the ability of a material to conduct electricity. 3. What materials are called conductors? 4. The materials that have very few or no free electrons are called insulators. 5. Electronics is defined in an English dictionary as "the study of conduction of electricity in a vacuum, in gases and in semiconductors". 6. When the cathode is heated, it emits electrons. 7. The electrons are repelled toward the plate by the negative voltage on the cathode. 8. If a negative voltage is applied to the plate, current does not flow.

 

13. Make up sentences from the following words. Put A in the Present Simple Passive, B – in the Present Continuous Passive.

A.

1. the/electrons/not/ attract/by/the/negative/voltage/on/the/ plate.

2. materials/classify/according/to/their/chemical/properties.

3. particles/can/set/in/motion?

4. not/on/it/ability/of/electricity/a/material/the/to/conduct/base.

5. flow/by/electrons/the/control/a/of/grid.

6. use/as/grids/amplifiers?

7. the/between/grid/place/the/cathode/and/the/plate.

8. not/such/call/semiconductors/materials.

9. the/more/the/better/you/will/words/translate/from/English/know/into/

Russian/you.

10. the/of/how/electrons/control/flow?

11. nowadays/the/losses/of/lighting/power/compensate/by/a/mirror/reflector.

12. conductors/materials/what/call?

B.

1. the/cathode/heat/by/the/heater.

2. the/current/make/to/flow/through/the/tube.

3. by/electrons/emit/cathode/the.

4. plate/the/current/decrease.

5. repel/the/toward/electrons/the/plate.

6. define/by/electronics/the/physicist.

7. to/voltage/a/negative/apply/the/plate.

8. of/electrons/the/describe/by/the/flow/student.

9. of/fundamentals/electronics/the/discuss.

10. semiconductors/and/and/insulators/consider/now/conductors.

Make questions to match the answers. All of them are in the Passive Voice.

For example:

Q – What is being discussed in the lecture room now?

A – The classification of materials is being discussed in the lecture room now.

1. Q – How …

A –Materials can be classified in many ways.

2. Q – What …

A – One of the ways is based on the ability of a material to conduct electricity.

3. Q – What particles …

A – Only charged particles inside the material can be set in motion.

4. Q – How …

A – Such materials are called conductors.

5. Q – Is …

A – The flow of electrons is being controlled.

6. Q – When …

A – The fundamentals of electronics are being discussed now.

7. Q – Who … by

A – The flow of electrons is being described by the student.

8. Q – What … with

A – The conductivity is being amplified with a number of new devices.

 

15. Match the following sentences with their translations. Which of them are in Passive?

1. Today we shall speak about classifying materials according to their electrical properties. 2. There are many ways of classifying materials. 3. The one we shall speak about is based on the ability of a material to conduct electricity. 4. Do only electrons take part in conductivity? 5. Сonductivity is the result of the motion of charged particles. 6. It is directly proportional to the number of charged particles inside the material that can be set in motion. 7. Only free electrons take part in conductivity. 8. Metals, for example, having many free electrons, can readily conduct current at room temperature. 9. Such materials are called conductors. 10.Other charged particles also take part in conductivity. 11.There are materials which have very few (or no) free electrons. 12.They are called insulators. 13. They have more free electrons than insulators, but fewer than conductors. 14. The higher the temperature, the lower the conductivity. a. Чем выше температура, тем ниже электропроводность. b. У них больше свободных электронов, чем у изоляторов, но меньше, чем у проводников. c. Они называются изоляторами. d. Cуществуют материалы, у которых мало (или совсем нет) свободных электронов. e. Другие заряженные частицы также принимают участие в электропроводности. f. Существует много способов классификации материалов. g. Такие материалы называются проводниками. h. Сегодня мы поговорим о классификации материалов по их электрическим свойствам. i. Металлы, например, имеющие много свободных электронов, могут легко проводить ток при комнатной температуре. j. Она прямо пропорциональна числу заряженных частиц внутри материала, которые могут быть приведены в движение. k. Электропроводность – это результат движения заряженных частиц. l. Только ли электроны принимают участие в электропроводности? m. Тот (способ), о котором мы будем говорить, основан на способности материала проводить электричество. n. Только свободные электроны принимают участие в электропроводности.

Choose as many words from the table оf ex. 1 as you can and form sensible sentences in Present Simple Passive and Present Continuous Passive (affirmative, negative and interrogative).

For example: The number of particles is unlimited.

Match the terms in Table A with their definitions in Table B

Table A Table B
1. classification 2. insulate 3. semiconductor 4. particle 5. conduction a. The process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material. b. A solid substance that has conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. Devices made of semiconductors, notably silicon, are essential components of most electronic circuits. c. The action or process of classifying something according to shared qualities or characteristics. d. Any of various fundamental subatomic and most basic constituents of matter, including those that are the smallest, and those that transmit one of the four fundamental interactions in nature (gravitational, electromagnetic, strong, and weak). e. Prevent the passage of electricity to or from (something) by covering it in nonconducting material.

18. Translate paying attention to the meanings of the word one.

For example: There are many ways of classifying materials. The one we shall speak about is based on the ability of a material to conduct electricity. – Существует много способов классификации материалов. Тот (способ), о котором мы будем говорить, основан на способности материала проводить электричество.

1. There are many types of robots; the ones, we are going to discuss today, are the robots of the 3-rd gen­eration.

2. The new computer is more powerful than the one put into service last year.

3. That semiconductor device is more efficient than the one under consideration.

4. Which of the gadgets is more useful than the new one?

5. There can be many schemes of different devices; the one given in Unit 2 shows the electron flow in a vacuum tube.

 

Change the form of the personal pronouns given in brackets.

For example: Physicists should work in order to realize (they) ambitions. - Physicists should work in order to realize their ambitions.

 

1. Today we shall speak about classifying materials according to (they) electrical properties.

2. There are many ways of classifying (they).

3. The one we shall speak about is based on (it) ability to conduct electricity.

4. Do only electrons take part in (it)?

5. Сonductivity is the result of the motion of (they).

6. It is directly proportional to the number of (they) inside the material that can be set in motion.

7. There are materials which have very few of (they).

8. Materials are classified according to (they) properties.

9. Many of (they) were discussed in the lab.

10. (It) number is not relevant.

11. The scientist (he) proved the results to be correct. He didn’t need help of any other staff.

12. (We) results in accomplishing this project were phenomenal.

13. These experiments were (they).

 

Make up sentences with personal pronouns on the topic of electronics and physics.

SPECIALIST READING

21. Read the text “Classifying Materials” and fill in the table.

Phenomenon Definition
Conductivity  
Conductor  
Semiconductor  
Insulator  

There are many ways of classifying materials. The one we shall use here is based on the ability of a material to conduct electricity. It is known that conduction takes place as a result of the motion of charged particles, usually electrons. The ability of any material to conduct electricity is directly proportional to the number of charged particles inside the material that canbeset in motion. Materials (for example metals) that have relatively large numbers of free electrons readily conduct electric current and are called conductors. Other materials having very few (or no) free electrons do not readily conduct electric current under normal conditions and are called insulators. Such materials as selenium, silicon and germanium have more free electrons than insulators, but fewer than conductors. They are called semiconductors. Conductivity depends on temperature. In metals the higher the temperature, the lower the conductivity. But in semiconductors, if the temperature rises, the conductivity increases but within certain limits. It should be realized1 that the terms “conductor” and “insulator” are not absolute, that is2 some conductors do not conduct as well as other conductors, while some insulators do not insulate as well as other insulators.

1 it should be realized – следует учесть 2 that is – то есть

Read the text again and complete the sentences with the correct beginning or ending.

1. … based on the ability of a material to conduct electricity.

2. Conduction takes place as …

3. The ability of any material to conduct electricity …

4. … are called conductors.

5. Materials having very few (or no) free electrons …

6. Semiconductors are materials …

7. The terms “conductor” and “insulator” are not absolute, that is

Work in pairs. Ask your partner questions based on the text. Make sure you use correct auxiliary verb.

1. Ways of classifying materials (How many?) …

2. The ability to conduct electricity (What?) …

3. As a result of (What?) …

4. Is directly proportional to (General question) …

5. Under normal conditions (Under what conditions?) …

6. Readily conduct electric current (How?) …

7. Such materials as selenium, silicon and germanium (How?) …

8. It should be realized (What?) …

24. Answer the following questions.

1. What is conduction?

2. What is conduction based on?

3. What groups are materials classified into according to their conductivity?

4. How does conductivity depend on temperature?

5. What materials are called: a) conductors, b) semiconductors, c) insulators?

SPEAKING

25. In groups finish the map based on the text “Classifying Materials” and use it while summarizing the text in 150 words.

Conductivity

 
 


You are at an international conference. Act as interpreters. Student A translates the description of the classification of materials made by his group mates from English into Russian and student B makes a reverse translation.

27. Translate the text “Energy Bands and Electrical Conduction” with a dictionary in writing paying attention to the use of the Passive Voice.

Electrons in semiconductors can have energies only within certain bands (i.e. ranges of levels of energy) between the energy of the ground state, corresponding to electrons which are tightly bounded to the atomic nuclei of the material, and the free electron energy, which is required for an electron to escape entirely from the material. Each energy band corresponds to a large number of discrete quantum states of electrons, and most of the states with low energy (closer to the nucleus) are full, up to a particular band. This one iscalled the valence band. Semiconductors and insulators are distinguished from metals because the valence band in semiconductor materials is nearly filled under normal operating conditions, thus causing more electrons to be available in the "conduction band," which is the one immediately above the valence band.

The ease with which electrons in a semiconductor can be excited from the valence band to the conduction one depends on the band gap between them, and it is the size of this energy band gap that serves as an arbitrary dividing line (roughly 4 eV) between semiconductors and insulators.

In the context of covalent bonds, an electron moves by hopping to a neighboring bond. According to the Pauli Exclusion Principle it has to be lifted into the higher anti-bonding state of that bond. In the context of delocalized states, for example in one dimension – that is in a nano wire, for every energy there is a state with electrons flowing in one direction and one state for the electrons flowing in the other. For a net current to flow some more states for one direction than for the other direction have to be occupied and for this energy is needed; in the semiconductor the next higher states lay above the band gap. Often this is stated as: full bands do not contribute to the electrical conductivity. However, as the temperature of a semiconductor rises above absolute zero, there is more energy in the semiconductor to spend on lattice vibration and – more importantly for us – on lifting some electrons into the energy states of the conduction band. The current-carrying electrons in the conduction band are known as "free electrons", although they are often simply called "electrons" if context allows this usage to be clear.

Electrons excited to the conduction band also leave behind them electron holes, or unoccupied states in the valence band. Both the conduction band electrons and the valence band holes contribute to electrical conductivity. The holes themselves don't actually move, but a neighboring electron can move to fill the hole, leaving a hole at the place it has just come from, and in this way the holes appear to move, and the holes behave as if they were positively charged particles.

One covalent bond between neighboring atoms in the solid is ten times stronger than the binding of the single electron to the atom, so freeing the electron does not imply destruction of the crystal structure.


Дата добавления: 2015-10-28; просмотров: 388 | Нарушение авторских прав


Читайте в этой же книге: Put all possible questions to the following statements. | Make sentences from the words in brackets using the Present Perfect Passive. | Act as an interpreter. Translate the description of N-type and P-type- semiconductors given by your group mates from English into Russian. | The P-N Junction | SPECIALIST READING | SPECIALIST READING | Work in pairs. Make up a dialogue, using the following questions and answers. |
<== предыдущая страница | следующая страница ==>
Degrees of Comparison| In Russian write a content-based summary of the text you have translated.

mybiblioteka.su - 2015-2021 год. (0.095 сек.)