Файл: Практикум по грамматике, чтению и переводу с английского языка Новосибирск 2008 Оглавление.doc

Cathode rays are widely used to draw information on television, computer and radar screens. In these devices, electrons are temporarily free as they move through the vacuum inside, for example, a television tube. However, if electrons are the normal constituents of atoms, how can they become free? To answer this question requires a little knowledge of atomic structure. Atoms are extremely small “bits” of material – millions of them would lie side by side across the diameter of a dot. At the core of an atom is a nucleus. The atomic particles are called protons and neutrons which have their home in the nucleus. Electrons, however, make up the electron cloud outside the nucleus. The nucleus is very small compared with the overall size of an atom. From the point of view of electronics, the most important properties of an electron are its electrical charge and its small mass. Its electrical charge means that it can be moved by an electric field, as in a telephone wire, or between the electrodes in a cathode ray tube. Its small mass means that the path of a beam of electrons can be rapidly deflected by electric and magnetic fields as in a television tube. An electron carries a negative charge and the proton an equal magnitude but positive charge. Since these charges are of opposite sign, the electrons remain in an electron cloud around the nucleus, each electron occupying a particular energy level. The neutron does not carry an electrical charge, i.e. it is said to be electrically neutral, and it does not have any part to play in making electrons stay in the electronic cloud. Electronics is to do with the use of semiconductors as well as conductors and insulators. Semiconductors are the basis of electronics devices such as transistors and diodes, heat sensors called thermistors, light-emitting diodes and integrated circuits. Semiconductor has an electrical resistance that falls somewhere between that of a conductor and an insulator. Two of the commonest elements from which semiconductors are made are the chemical elements silicon and germanium. Silicon is abundant in the Earth′s crust and is present in sand and glass. Both elements are important in electronics because their resistance can be controlled to produce useful semiconductors. This is achieved by adding minute amounts of carefully selected substances to them, a process called doping. Once a very pure crystal of silicon has been manufactured, the silicon is doped with impurity atoms to make useful semiconductors! These impurity atoms are chosen so that they make a “bad fit” in the crystal structure of silicon, due to the impurity atoms having too many or too few electrons in their outer shells. Depending on the impurity atoms, two types of semiconductor are produced in this way, n-type or p-type. If silicon is doped with, for example, phosphorus atoms, an n-type semiconductor is produced. This arises because a phosphorus atom has five electrons in its outer shell. It happens when an atom of phosphorus is embedded in the crystal structure of pure silicon. Four of the five outer phosphorus electrons form covalent bonds with neighbouring silicon atoms, leaving a fifth unpaired electron. This unattached electron is now weakly bound to its parent phosphorus atom and it is therefore free to wander off and contribute to current flow through the semiconductor. Phosphorus is said to be a donor impurity since each atom of phosphorus can donate an electron. The addition of phosphorus has therefore changed the electrical properties of silicon. It has become an electrical conductor, not a good one but semiconductor, due to the presence of free electrons donated by phosphorus atoms. Thus, the “n” in n-type semiconductor denotes the contribution electrons make to current flow through this semiconductor and are known as majority charge carriers. There are also a very few electrons and holes produced by the effect of heat, that breaks covalent bonds between silicon atoms. The holes in an n-type semiconductor are called minority charge carriers. The contribution of minority charge carriers to the current that flows in n-type semiconductor is negligible, but note that the holes flow in the opposite direction to the electrons. By doping silicon with atoms such as boron that have three electrons in their outer shells, a p-type semiconductor is produced. Three of its outer electrons become paired with neighbouring silicon atoms, leaving one unpaired silicon electron. The vacant space will accept another electron. The vacancy created in silicon by doping it with boron is known as a hole. Since this hole attracts an electron, it behaves as if it had a positive charge. Boron is said to be an acceptor impurity since it creates a vacancy in the crystal structure enabling it to accept an electron. The presence of holes acting as positive charges in boron-doped silicon produces a p-type semiconductor (“p” for positive).

Vocabulary:

constituent – составная часть, составляющая

particle – частица

overall – полный, общий, предельный

magnitude – величина, размер

to deflect – отражать

shell – оболочка

abundant – избыточный

minute – крохотный, мелкий, незначительный

thermistor – терморезистор

heat sensor – тепло-чувствительный элемент

to embed – впитывать посторонние смеси, погружать, внедрять

acceptor – акцептор (тип примеси в полупроводнике)

doping – добавление примесей

impurity – примесь

to donate – выпустить

negligible – незначительный

hole – дырка

bond - связь, соединение

X. Find the Infinitives in the text and define their functions.

XI. Read the text again and answer the questions.

State two examples of materials that are electrical insulators and two examples of materials that are electrical conductors.
Describe the simple model of an atom.
Describe he process which is called doping.
What does the type of semiconductor depend on?
An element widely used in the manufacture of semiconductors is silicon/carbon/iron?
What does “n” in n-type semiconductor denote?
What does “p” in p-type semiconductor denote?
Explain how silicon becomes a p-type semiconductor when it is doped with boron.
Explain how silicon becomes an n-type semiconductor when it is doped with phosphorus.

XII. Read the text again and decide whether these statements are true or false.

Electrons don′t make up the electron cloud outside the nucleus.
Free electrons must be present in a material if they are to conduct electricity easily.
A small mass of an electron means that the path of a beam can be slowly deflected by electric field.
The neutron does not carry an electrical charge.
Semiconductor is the basis of light emitting diodes.
The holes flow in the same direction as electrons do in an n-type semiconductor.
Boron is an acceptor impurity because it creates a vacancy in the crystal structure.

XIII. Complete the sentences using the correct variant.

In electronic devices electrons

can′t be free;
can be free.

The most important properties of an electron are

its electrical charge and small mass;
its electron cloud and nucleus.

The path of a beam of electrons

can be deflected;
can′t be deflected.

The electrons remain in an electron cloud around the nucleus because the electron and proton charges

are of the same sign;
are of opposite sign.

Silicon and germanium are very important because their resistance

can be controlled to produce useful semiconductors;
falls somewhere between that of a conductor and an insulator.

XIV. Combine words from Box A with words from Box B to make collocations.

A

impurity

outer

covalent

crystal

atomic

heat

B

shells

bond

atom

sensor

structure

particle

Смотрите также файлы

Перечень лабораторного оборудования и наглядных пособий для кабинета физики средней школы (711 классы) (до 30 учащихся).doc

Валентина Владимировна Терешкова одна из самых значимых личностей двадцатого века родилась в семье белорусов 6 марта 1937 года в селе Масленниково, что расположено в тридцати километрах от Ярославля.docx

Решение педагогической задачи План.docx

Научноисследовательская работа (тип практики) 8 семестр обучающегося группы (Шифр и группы) ( фио обучающегося) Место прохождения практики Университет Синергия.docx

Верясова Д. Д.docx

Файл: Практикум по грамматике, чтению и переводу с английского языка Новосибирск 2008 Оглавление.doc

Example: I can′t buy this computer. It is too expensive for me.

This computer is too expensive for me to buy.

Nobody could move the piano. It was too heavy.

The piano …

I can′t explain the situation. It is too complicated.

The situation …

You can′t see some things without a microscope. They are too small.

Some …

4. Light beam of a laser can vaporize the hardest and most heat-resistant materials. It is intensive enough.

Light beam …

I can′t use the “night vision” system in my automobile. It is not small enough.

The “night vision” system …

IX. Read the text. Express the main idea of the text. Translate it.

Electrons in atoms

constituent – составная часть, составляющая

particle – частица

overall – полный, общий, предельный

magnitude – величина, размер

to deflect – отражать

shell – оболочка

abundant – избыточный

minute – крохотный, мелкий, незначительный

thermistor – терморезистор

heat sensor – тепло-чувствительный элемент

to embed – впитывать посторонние смеси, погружать, внедрять

acceptor – акцептор (тип примеси в полупроводнике)

doping – добавление примесей

impurity – примесь

to donate – выпустить

negligible – незначительный

hole – дырка

bond - связь, соединение

X. Find the Infinitives in the text and define their functions.

XI. Read the text again and answer the questions.

State two examples of materials that are electrical insulators and two examples of materials that are electrical conductors.

Describe the simple model of an atom.

Describe he process which is called doping.

What does the type of semiconductor depend on?

An element widely used in the manufacture of semiconductors is silicon/carbon/iron?

What does “n” in n-type semiconductor denote?

What does “p” in p-type semiconductor denote?

Explain how silicon becomes a p-type semiconductor when it is doped with boron.

Explain how silicon becomes an n-type semiconductor when it is doped with phosphorus.

Electrons don′t make up the electron cloud outside the nucleus.

Free electrons must be present in a material if they are to conduct electricity easily.

A small mass of an electron means that the path of a beam can be slowly deflected by electric field.

The neutron does not carry an electrical charge.

Semiconductor is the basis of light emitting diodes.

The holes flow in the same direction as electrons do in an n-type semiconductor.

Boron is an acceptor impurity because it creates a vacancy in the crystal structure.

XIII. Complete the sentences using the correct variant.

In electronic devices electrons

can′t be free;

can be free.

The most important properties of an electron are

its electrical charge and small mass;

its electron cloud and nucleus.

The path of a beam of electrons

can be deflected;

can′t be deflected.

The electrons remain in an electron cloud around the nucleus because the electron and proton charges

are of the same sign;

are of opposite sign.

Silicon and germanium are very important because their resistance

can be controlled to produce useful semiconductors;

falls somewhere between that of a conductor and an insulator.