The Concept of Electrical Current
In the beginning of the 171 century Sir William Gilbert discovered that many substances could be electrified by friction. Gilbert named this effect "electric" after the word "electron" - the Greek name for amber. In 1756 the Great Russian scientist M.V. Lomonosov was the first to make theoretical analysis of electrical phenomena.
At present the nature of electrification is explained by the electron theory.
According to the modern theory all matter is composed of atoms or tiny particles. There are many kinds of atoms. Each atom consists of a nucleus, a small positively charged mass and a number of lighter negatively charged particles called electrons, which revolve around the nucleus. Normally each atom of a substance is electrically neutral, or it has equal amounts of negative and positive charges, i.e. produces no electrical effects. If the number of negative charges is not equal to the number of positive charges, the matter will produce electrical effects.
When an electric charge is at rest it is spoken of as static electricity, but when it is inmotion it is referred to as an electric current. An electric current is described as a flow of electric charges along the conductor.
Metals are good conductors of electricity, whereas nonmetals are poor conductors. The poorest of conductors are called insulators or nonconductors. There are a large number of substances that are neither good conductors of electricity nor good insulators. These substances are called semi-conductors. An electric current, which flows in the same direction through a conductor or current, which doesn't change its polarity, is called a direct current or a continuous current. Its abbreviation is D.C. An alternating current (A. C.) flows first inone direction and then in the other.
An electric circuit is a path through which an electric current flows. This is a complete path along which electrons can transmit their charges. An electric circuit includes a battery, generator, or magnetic means I for producing current flow. Some portion of the current is made to do useful work.
llhecircuit is opened when no charges can move due to a break in the path. The circuit is closed when I no breaks exist - when switches are closed and all connections are properly made. Special symbols are used to show electrical systems.
Wordlist
particle частица
nucleus ядро
chargeзаряд
electriccurrent электрический ток
conductorпроводник
insulator диэлектрик
direct (alternating) current постоянный(переменный) ток
electric circuit электрическая цепь
amber янтарь
Контрольная работа № 2 Вариант № 3
Переведите предложения с модальными глаголами и их заменителями.
. We can measure voltage and potential difference with a voltmeter. 2. What instrument may we usein measuring current? 3. He willbe able to draw a circuit diagram. 4. They might know safety rules. 5. He lad to remember properties of metals. 6. You must_dothis work in time.
. II. Вы собираетесь строить дом. Составьте рекомендации, употребив глаголы в
повелительном наклонении:
0 make a design, to choose the right place, to work hard, not to forget about the landscape, to choose
modern building materials, to calculate money
III. Перепишите и переведите письменно предложения и словосочетания, обратите внимание
на многозначность предлогов.
I. We must try to bring the government down. 2. The new government promises to bring down prices. 3. How did you bring it off?4. Our firmis bringing out a new product. 5. There are a lot of interesting places in our town. 6. We are going<on an excursion around the town.
IV. Перепишите предложения, подчеркните инфинитив и инфинитивные обороты; переведите
предложения на русский язык.
1.1 can't for the weather to change. 2. I want you to tell me all you know about him. 3. I'llmake him tell (he truth. 4.1 saw children cross the street when the light was red. 5.1 shall be happy to do it for you. 6. She seems to know a lot about music.
V. Определите, от каких частей речи образованы выделенные слова; переведите предложения
на русский язык.
1They are quite different.2. What is the differencebetween "town" and "city"? 3. There is a lot of
violenceon TVnow. 4. Chemistryis my hobby. 5. He is a chemistby profession. 6. The weather is very
changeable this spring.