Types of electricity

Unit 3

ELECTROMAGNETISM

Tunung-in

Task 1Discuss the questions using your knowledge of physics.

1) What is electricity?

2) What determines the conduction of electricity?

3) Why are metals good conductors? Which are the best conductors?

4) Do gases conduct electricity?

5) What are the different types of electricity?

6) What is a major advantage of AC electricity?

Reading I

Basics of Electricity

Task 2 You are going to read the text about electricity. Seven sentences have been removed from it. Choose from sentences A-G the one which fits each gap (1-7). There is an example at the beginning. Then check your answers to the questions of Task1.

A Gases are not good conductors of electricity because of the distances between atoms.

B This is the type of electricity that comes from the outlets in most homes.

C This flow of electrons through the conductor is electricity.

D Often the electrons are pulled from the atoms on one surface and allowed to collect on the surface of another material.

E It has the advantage of being able to have its voltage easily changed to a higher or lower level.

F The conduction of those electrons is determined by the type of material.

G This allows free electrons to roam about the material.

Electricity is the movement of free electrons in a material toward an area of positive (+) charges. 1_G__ ( The conduction of those electrons is determined by the type of material.) Some conduct well, while other materials prevent the movement of electrons. Electricity can take the form of static electricity, direct current (DC) electricity, or alternating current (AC) electricity.

Conduction of electricity

Solid metals are good conductors of electricity, because electrons are allowed to move freely throughout the material. In the solid state, the atoms of metals are held in place and only vibrate. 2____ Copper and gold are some of the best conductors of electricity. Although iron is a good conductor, iron oxide (rust) is not.

In semi-conductors—such as materials used in computer chips—the electrons have limitations to their movement, such as only being allowed to move in one direction or in one plane.

Nonconductors inhibit the movement of electrons within the material. But they often do allow electrons and ions to collect on their surfaces. Examples of nonconductors or electrical insulators are: plastic, rubber, glass, most metal oxides (like rust), air, oil, pure de-ionized water. 3____ Electrons have difficulty moving through gases, unless the gas is ionized or heated to higher temperatures.

Types of electricity

Common types of electricity are static electricity, direct current (DC) electricity and alternating current (AC) electricity.

Static electricity is the collection of free electrons on the surface of a material, giving it a negative (−) charge. Atoms on the surface of another material that have lost one more of their electrons are called positive (+) ions. 4____ Static electricity is caused by rubbing the two different materials together. Since opposite charges attract, there is a tendency for the electrons to attract toward the positive ions, resulting in static electricity.

In a metal or other conducting material, electrons will flow from an area of an excess negative (−) charges to an area of positive (+) charges. 5____ If the opposite charges are constant, such as with the terminals in a battery, the current is called direct current or DC electricity, because it is going in one direction. If the terminals constantly switch their polarity from (+) to (−) and back again, the direction of the electrons alternates and is call alternating current or AC electricity. 6 ____

DC can be created by a battery or DC generator. AC requires an AC generator for its creation. DC is used in many devices that do not require high voltages for their operation, such that batteries are used for power. AC can be used in higher voltages. 7____ AC is required for many electronic devices.

Language study

Task 3

Read the extract. Underline the subject and the predicate of the sentences in bold type.

Task 4

What part of speech are these words in the given extract - nouns or verbs?

Put N for a noun and V for a verb:

flows, heats, glows, link, lights, sets, discharge,force,decrease,act.

Everyday modern life is pervaded by electromagnetic phenomena. When a light bulb is switched on, a current flows through a thin filament in the bulb; the current heats the filament to such a high temperature that it glows, illuminating its surroundings. Electric clocks and connections link simple devices of this kind into complex systems such as traffic lights that are timed and synchronized with the speed of traffic. Radio and television sets receive information carried by electromagnetic waves traveling through space at the speed of light. To start an automobile, currents in an electric starter motor generate magnetic fields that rotate the motor shaft and drive engine pistons to compress an explosive mixture of gasoline and air; the spark initiating the combustion is an electric discharge, which makes up a momentary current flow.

Many of these devices and phenomena are complex, but they derive from the same fundamental laws of electromagnetism. One of the most important of these is Coulomb’s law, which describes the electric force between charged objects. Formulated by the 18th-century French physicist Charles-Augustin de Coulomb, it is analogous to Newton’s law for the gravitational force. Both gravitational and electric forces decrease with the square of the distance between the objects, and both forces act along a line between them.

Grammar Study

Date: 2016-01-03; view: 2447