Lesson 3. Electricity

TEXT 3 A. Electricity;

Grammar Exercises (The Participles. The Absolute Participle Construction. The Functions of the Participles);

TEXT 3 B. Transformers;

TEXT 3 C. Electric Current in a Vacuum.

Pre-Text Exercises

Active Vocabulary

I. Practise reading the words written below. You’ll come across them in text 3a.

electricity at rest …….. electricity in motion … charge ……………….. to differ ……………… lightning …………….. rubbing ……………… substance ……………. dissimilar ……………. observation ………….. pressure ……………… to obtain ……………... source ……………….. voltaic pile …………... copper ……………….. layer …………………. flannel ……………….. to moisten …………… circuit ………………... direct current ………… alternating current …… to conduct …………… voltage ………………. attainment …………… definite ………………. successive …………… frequency ……………. radar …………………. to step down …………. purpose ………………

статическое электричество электрический ток заряд различать молния трение вещество разнородный, неодинаковый наблюдение давление получать источник гальваническая батарея медь пластина фланель увлажнять, смачивать цепь постоянный ток переменный ток проводить напряжение достижение определенный последовательный частота радиолокационная установка понижать (напряжение) цель

II. Put the words from the box into the correct columns. Translate them into Russian.

dissimilar, condition, ability, negative, continuous, easily, inexpensive, transformer, pressure, layer, successive, evident, attainment, receiving, direction, commercial, environment, trying

Noun (what / who?)	Adjective (what kind of?)	Adverb (in what manner?)	Participle (which?)
electricity …	… electric	…	…

III. Read text 3a. Try to understand its content. Text 3 a. Electricity

There are two types of electricity, namely, electricity at rest or in a static condition and electricity in motion, that is, the electric current. Both of them is made up of electric charges, static charges being at rest, while electric current flows and does work. Thus, they differ in their ability to serve mankind as well as in their behaviour.

Let us now turn our attention to the early facts, that is to say, let us see how it all started.

History shows us that at least 2.500 years ago, or so, the Greeks were already familiar with the strange force being known today as electricity. Three phenomena made up all of man’s knowledge of electrical effects: (1) lightning flash; (2) the process of rubbing; and (3) so-called electric fish. As we have mentioned, the Greeks knew how to get electricity by rubbing substances, however, the electricity being obtained by rubbing objects can’t be used to light lamps, to boil water, to run electric trains. As early as 1753, Franklin was the first to prove that unlike charges are produced due to rubbing dissimilar objects. Showing that the charges are opposite, he decided to call the charge on the rubber – negative and that on the glass – positive. Petrov was the first to carry on experiments and observations on the electrification of metals being rubbed one against another. And he was the first scientist in the world who solved that problem. Who doesn’t know that the first man having got the electric current was Volta after whom the unit of electric pressure, the volt, was named? His discovery developed out of Galvani’s experiments with the frog. Galvani observed that the legs of a dead frog jumped as a result of an electric charge. Having tried his experiment several times he obtained the same result. He thought that electricity was generated within the leg itself. Volta began to carry out similar experiments and soon found that the electric source wasn’t within the frog’s leg, but was the result of the contact of both dissimilar metals used during his observations. The scientist spent the next few years trying to invent a source of a steady, continuous current. To increase the effect obtained with one pair of metals, Volta increased the number of these pairs. Thus the voltaic pile consisted of a copper layer and a layer of zinc placed one above another with a layer of flannel moistened in salt water between them. A wire was connected to the first disc of copper and the last disc of zinc. The year 1800 is a date to be remembered: for the first time in the world’s history a steady, continuous current was generated.

Current is a flow of electricity through a circuit. Let us consider two main types of current: direct and alternating. Current flowing through a conducting circuit in one direction only is a direct current (d.c.). It flows provided a direct voltage source is applied to the circuit.

Current changing its direction of flow through a circuit is named as an alternating current (a.c.). It flows provided an alternating voltage source is applied to the circuit. Alternating current flows in cycles. The interval of time between the attainment of a definite value on two successive cycles is called the period; the number of cycles or periods per second is the frequency, and the maximum value in either direction is the amplitude of the a.c. Low frequencies, such as 50 and 60 around 100.000,000 cycles per second (100 megahertz) are used in television and of several thousand megahertz in radar or microwave communication. It is easy to transform a. c. power from one voltage to another by a transformer. Transformers are also used to step down the voltage at the receiving point of the line to the low values that are necessary for use.

The evident advantage of electricity is that it doesn’t pollute environment, inexpensive and easily transmitted over long distances. Since the 1880’s, electricity has had an ever-increasing role in improving the standard of living. It has been counted that in developed countries about 43% of the electric power is generally used for industrial purposes, 32% in homes, and 21% in commercial enterprises.