PRIMARY INVESTIGATIONS. CLASSES OF ELECTRICITY

lt was known since the ancient Greeks that when а piece of amber or glass is rubbed with silk or fur, it achieves the power of attracting light objects. Later on, this phenomenon was studied and the word ‘electric’ (after Greek «electron» — «amber») was put in use.

During the 18-191h centuries many discoveries about the nature of electricity were made: Charles Coulomb investigated the forces between the charged objects; Benjamin Franklin invented the lighting rod, etc.

There was developed the idea that there are two kinds of electricity, which were called resinous electricity, and that opposite kinds of electricity attract one another, whereas similar kinds repel one another.

The study of electricity may Ье divided into three classes ( or branches):

magnetism;

electrostatics;

electrodynamics.

Magnetism is the property of the molecules of iron and other certain substances due to which they store energy in а field because of the arranged movement ofthe electrons in their atoms.

Electrostatics is the study of electricity at rest, or static electricity. Examples ofthis type of electricity are charges on condenser plates. Rubblng glass with silk produces static electricity.

Electrodynamics is the study of electricity in motion, or dynamic electricity. The electricity which flows through wires for light and power purposes is а good example ofthe latter type of electricity.

ПЕРВИЧНЫЕ ИССЛЕДОВАНИЯ. КЛАССЫ ЭЛЕКТРОЭНЕРГИИ

Еще со времен древних греков было известно, что, если натереть кусок янтаря или стекла шелком или мехом, он приобретает способность притягивать легкие предметы. Позднее это явление было изучено и в обиход вошло слово «электрический» (от греческого «электрон» — «янтарь»).

В течение 18-191х веков было сделано много открытий о природе электричества: Шарль Кулон исследовал силы между заряженными объектами; Бенджамин Франклин изобрел громоотвод и т. д.

Существовало представление о том, что есть два вида электричества, которые назывались смолистым электричеством, и что противоположные виды электричества притягиваются друг к другу, тогда как сходные виды отталкиваются друг от друга.

Изучение электричества можно разделить на три класса (или ветви):

магнетизм;

электростатика;

электродинамика.

Магнетизм есть свойство молекул железа и других определенных веществ, благодаря которому они запасают энергию в поле из-за упорядоченного движения электронов в их атомах.

Электростатика изучает электричество в состоянии покоя или статическое электричество. Примерами этого вида электричества являются заряды на пластинах конденсатора. Натирание стекла шелком производит статическое электричество.

Электродинамика изучает электричество в движении или динамическое электричество. Электричество, которое течет по проводам для освещения и питания, является хорошим примером последнего типа электричества.

EXERCISES

Check yourself in your vocabulary.

What do you call:

the property of the molecules of iron to store energy in а field? magnetism

the study of electricity at rest? electrostatics

the study of electricity in motion? Electrodynamics

а piece of iron or steel which being magnetized retains its magnetism? magnit

the method of producing electricity based on operation of rotating generators in which electricity is produced by conductors moving through а magnetic field? Electromagnetic method

а movement of charges? Conduction

а driving force making electrons move trough а metal conductor? Electromotive force

an electtric current that doesn ‘t change its direction and magnitude? Direct current

an electric current that changes both its direction and magnitude at fixed intervals of time? Alternating current

an electric current alternative in its magnitude and stable in its direction? Pulsating current

an electric unit intended for measuring the strength of electric current in а circuit? ampere

а device used for measuring resistance? ohmmeter

а device used for measuring insulation resistance? megohmmeter

an extemal force applied to а circuit to overcome the opposition to the flow of current? Electromotive force

а device used for measuring voltage? voltmeter

devices intended for measuring delivery of electric energy in watts? wattmeter and watthourmeter

Make sure уou ‘ve grasped the contents of the texts given above:

There was developed the idea that similar kinds of electricity:

а) attract each other;

b) repel one another;

с) attract small pieces of iron.

Electrodynamics studies:

а) electricity at rest;

b) random movement of free electrons;

с) electricity in motion.

Examples of static electricity are:

а) charges on condenser plates;

b) magnetic lines of force around the wire;

с) ions moving in liquid conductors.

Each of permanent magnets has:

а) а north pole only;

b) а south pole only;

с) both а north and а south poles.

Permanent magnets are used for producing the magnetic field necessary for operation of:

а) ship’s electric propulsion plants;

b) small electrical motors;

с) generators of al\lsizes.

In electrical circuits the flow of electric charges is а flow of:

а) electrons;

b) positive charges;

с) ions.

When the e.m.f. is applied to the ends of the wire:

а) positive charges move in оnе direction;

b) free electrons move in random manner;

с) free electrons move in оnе direction.

According to Ohm’s law applied to the entire circuit the strength of the current is:

а) inversely proportional to the e.m.f. аnd directly proportional to the resistance of the circuit;

b) directly proportional to the e.m.f. аnd inversely proportional to the resistance of the circuit;

с) inversely proportional to the e.m.f. and to the resistance of the circuit.

The strength of the current in а.с. circuits depends оn:

а) the resistance of the circuit and the voltage applied to it оnlу;

b) the resistance of the circuit and the inductance. and capacitance of the circuit section;

с) the resistance of the circuit, the voltage applied to it, the inductance and capacitance of. the circuit sections.

With the increase in the temperature the resistance of аll metals:

а) decreases;

b) increases;

с) remains unchangeble.

III Mind your Grammar.

Put the verbs in brackets in the correct form — Present or Past Simple Active.

The study of the nature of electricity began in the 18th century.

Rubbing glass with silk produces static electricity.

Electromotive force makes electrons move through а conductor.

The experiment held yesterday proved that these substances showed different resistances.

If you want to measure insulation resistance, you use «megger» .

Voltage overcomes the opposition to the flow of current.

Many scientists investigated electric phenomena in the 19th century.

Electrons move under the influence of e.m.f.

Ohm’s law gives the possibllity to measure electric current in а circuit.

After some experiments the scientists defined the law of measuring three basic electrical units.

Charges in motion give rise to а magnetic field.

Michael Faraday discovered magnetic induction.

When the current stops, the magnetic field also disappears.

Loudspeakers and electric motors are examples of application of magnetism.

The principal utilization of electricity increased rapidly with the development of telegraph in 1844, electric motors in 1887 etc.