Basic Solid-State Principles

In a conductor, electric current flow is a movement of free electrons. The outer or valence electrons of a good conductor are loosely bound to the atom. At room temperature the thermal energy causes approximately one

electron to detach from each atom and become free to move and result in a current flow when an electric potential is applied.

Insulators are materials in which outer electrons are tightly bound to the atom and no electrons are free to move. Thus, no current can flow when voltage is applied.

Between these two major categories is a class of materials called semiconductors. As the name implies, a semiconductor is a material with conductivity roughly midway between conductors and insulators. It is not just a poor conductor; it has two important properties. First, its resistance normally decreases with increase of temperature, while in conductors resistance slightly increases with temperature. Second, the flow of current in a semiconductor may be caused either by a flow of negative electrons or by a movement of missing sites in the opposite direction. If an atom has one outer electron missing, a loosely bound electron from a neighbouring atom can jump into it, leaving behind a new vacant site; this, in turn, can be filled by an electron from the third atom and so on. The impression is as if the vacant site has moved. Such vacant sites are called “holes” and since a negative electron is missing, the hole can be said to have a positive charge.

Semiconductor materials in which conduction is due to a flow of electrons are called n-type materials and those in which conduction is due to the movement of positive holes are called p-type.

Вариант 2

1. Вставьте в предложения глагол to be в форме единственного или множественного числа is/are.

1.Where … the money? 2.His trousers … too large for him. 3.Mathematics … my poorest subject. 4.His savings … in the bank. 5.Those glasses … his.

2. Употребите в данных предложениях личные местоимения.

1.This is my new coat. Look at … . 2.My uncle is old. He wants to live with … and my parents. 3.How is your nephew? Say “Hi” to … . 4.You are ill, Pete. We want to be with … in the evening. 5.Mary and I are good students, so our teacher likes … . 6.Linda isn’t here. Can I give … a message?

3. Заполните пропуски притяжательными местоимениями в простой или абсолютной форме.

1.I have a dog. The dog is … . 2.I have a piano in … room. 3.Tell him not to forget … paper, she must not forget …, either. 4.I managed to keep … books dry, but you got … wet, I see. 5.Sarah is dressed very well. Most of … clothes are expensive. 6.Jim has left. These cannot be … keys.

4. Перепишите и письменно переведите предложения, обращая внимание на перевод неопределенных местоимений и наречий.

1.Some electronic devices find wide application in every house. 2.You will find this material nowhere but in the encyclopedia. 3.Something happened to my computer. It doesn’t work. 4.Any result in our experiment will be of great importance for the whole research. 5.If you have no money, you cannot buy anything. 6.She said nothing. 7.There was no one in the room.

5. Напишите форму множественного числа от данных существительных:

piano, knife, woman, child, deer, classroom, manservant, brother-in-law, bench, day, trout

6. Поставьте выделенные существительные во множественное число. Произведите все необходимые изменения.

1.This is an English dictionary. 2.The last leaf fell from the tree. 3.Where is the brush? 4.The roof of the house with covered with snow. 5.There is a sheep in the field. 6.There is an angry wolf in the forest.

7. Перепишите данные ниже предложения. Определите по

грамматическим признакам, какой частью речи является слово, оформленное окончанием -s, какую функцию это окончание выполняет, т.е. служит ли оно а) показателем 3л.ед.ч. в Present Indefinite (Present Simple), б) признаком множественного числа существительного, в) показателем притяжательного числа имени существительного. Предложения переведите.

1.The St. Petersburg technical University trains specialists in many fields. 2.Trains from Moscow arrive in St. Petersburg at the Moscow Railway Station. 3.Flats in new houses are very comfortable. 4.The Hermitage houses a big collection of Western European Art. 5.This problem needs a special approach. Our country’s needs in electricity will continue to grow.

8. Вставьте вместо точек s, ‘s, s’, где необходимо.

1.This man was Paul… and Kate… teacher… of music. 2.My relatives spent a two week… holiday with the Barton… . 3.This winter… life was short but bright. 4.The boy… got their first week… salary and were very happy.

9. Перепишите следующие предложения, содержащие разные формы сравнения, и переведите их на русский язык.

1.There are more than 50 schools of higher learning in St. Petersburg. 2.Mathematics is as important for technical students as Physics. 3.This new apparatus is 4 times as powerful as the old one. 4.These machine tools are not so efficient as the new ones. 5.The more systematic are our studies, the deeper is our knowledge.

10. Раскройте скобки и поставьте прилагательные в нужную степень.

1.Of the two sisters Mary is the (beautiful). 2.Which do you like (good), orange juice or lemon juice? 3.The Nile is the (large) river in Africa. 4.Let’s go by car. It’s (cheap) than by train. 5.This is (comfortable) room in my flat. It is (big) and (light) than other rooms. 6.Kate is the (young) of my five sisters.

11. Перепишите данные предложения, определите в них видо-временные формы глагола и укажите их инфинитив. Предложения переведите.

1.There is a wide system of extramural education in our country. 2.In two years, my friend will become a specialist in the field of radio engineering. 3.She got up, washed, had breakfast and went to school. 4.Our classes begin at 8.30. 5.We saw an interesting film yesterday.

12. Перепишите и переведите приводимые ниже предложения. Поставьте их в отрицательную форму. Задайте общий и специальный вопросы к каждому предложению.

1.The Wilsons normally have breakfast at 7 o’clock. (When?) 2.Many people like to work in the garden. (Where?) 3.They went to the airport by car. (How?) 4.They chose books and magazines at the bookstall. (What?) 5.I shall know the result in a week. (When?) 6.He will buy a present to Mary for Christmas. (To whom?)

13. Прочтите и устно переведите текст. Перепишите и письменно переведите 2-й абзац текста.