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Exercise 1. Listen as you read the text.

Electricity is one of the basic forms of energy. Electricity is associated with electric charge, a property of certain elementary particles such as electrons and protons, two of the basic particles that make up the atoms of all ordinary matter. Electric charges can be stationary, as in static electricity, or moving, as in an electric current.

The charges are free electrons (in metals) or ions (in liquids and gases). We can easily understand the nature of the electric current on the basis of electron theory. An atom is a complex particle in which tiny electrons move around a nucleus. In metals some of the electrons move freely among the atoms. There are free electrons. The electromotive force causes the electrons to move through the metal conductor.

There are two types of the electric current, namely, the direct current (d. c. for short) and alternating current (a. c.). The electric current can heat a conductor, it can have chemical action, or it can produce the magnetic effect.

The electric current starts to flow from a battery or a generator, passes through wires, lamps, meters and other resistance and returns to its starting point. All these devices and conductors constitute the circuit. A steady electric current, like a water current, has the same value at all parts of a simple unbranched circuit.

The electric current flows only when there is a different of potential between the two points in the circuit. The opposition to the current flow is the resistance. Thus we can say that the current is directly proportional to the voltage and inversely proportional to the resistance (Ohms law).

There are special units of measurement of electric quantities. The ampere is a unit of rate of flow of electric current. The ampere indicates the amount of electric current. The volt is a unit of electrical pressure. The international volt creates a current of one international ampere in a conductor, which has a resistance of one international ohm. The watt is a unit of power, which electric devices develop. One watt is equal to a current of one ampere as a result of one volt.

We measure these electrical quantities with the help of special instruments named as measuring devices. We measure current with ammeter, voltage with voltmeter and power with wattmeter.

Ammeters measure the current flowing in a circuit and normally have scales graduated (or calibrated) in amperes, milliamperes, or microamperes. The ammeter has a low resistance coil not to absorb an appreciable amount of power; therefore, we connect the ammeter into a circuit in series.

Voltmeters measure the potential difference between the two points in a circuit. We connect a voltmeter in parallel across the points where it is necessary to measure the difference of potential. The resistance of voltmeter operation coil is as high as possible to limit the amount of power consumed by it.

Exercise 2. Answer the questions.

1) What forms of energy do you know?

2) Why electricity is the most important form of energy in modern technologies and everyday life?

3) What are the common sources of electric current?

4) What do you think are advantages and disadvantages of different forms of electric current, direct and alternating?

5) What are the main sources of electricity in this country?

6) What main rules of electric current do you know?

7) What types of measuring instruments are employed to fix damages in electric lines?

Exercise 3. Work in pairs. Find out if your classmate

1) used to work with some electrical instruments.

2) didnt use to like learning laws of electricity in school.

3) has to study tomorrow.

4) has a million things to do after class.

5) knows the latest weather forecast.

Date: 2015-12-11; view: 606

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