VIII.A) Прочтите текст и ответьте на следующие вопросы:
1.What was the greatest invention created by Nicola Tesla?
2.How many inventors and patents had Tesla at the end of his career?
б) Переведите в письменной форме абзацы 1, 2.
THE ELECTROMAGNETIC MOTOR
1. Born in Croatia, the engineer Nikola Tesla had a distinguished academic and industrial career in central and eastern Europe before coming to the United States in 1884. Here, while working for the Edison Machine Works and independently, Tesla created his greatest invention, the electromagnetic motor.
2. A motor converts electrical energy to mechanical power by using current to make a metallic loop ("the rotor" or "armature") spin around a central shaft. Tesla was convinced that DC ("direct current") motors could be modified to operate without commutators. In early 1888, working out of his experimental shop in New York, he proved his theory: Tesla built and demonstrated the "induction" or "electromagnetic" motor, Tesla's revolutionary motor used a rotating magnetic field, rather than mechanical switches, to spin the rotor. This made unit drives for machines possible, and allowed the more efficient AC ("alternating current") power to become the standard for most office and household appliances,
3. Tesla was also a pioneer in the early days of radio (invented by Guglielmo Marconi at the turn of the century).
4. By the end of his career, Tesla had over 700 inventions and 100 patents to his credit. Though his innovations never made him wealthy, Tesla is rightly renowned to this day as one of the greatest electrical engineers of all time.
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Text 1
An electric cell is used to produce and supply electric energy. It consists of an electrolyte and two electrodes. Electrodes are used as terminals, they connect the cell to the circuit - current passes through the terminals and the bulb lights.
Cells can be connected in series, in parallel and in series-parallel. In order to increase the current capacity cells should be connected in parallel. In order to increase the voltage output cells should be connected in series. In case a battery has a large current capacity and a large voltage output, its cells are connected in series-parallel.
When cells are connected in series the positive terminal of one cell is connected to the negative terminal of the second cell, the positive terminal of the second cell-to the negative terminal of the third ... and so on.
When cells are connected in parallel their negative terminals are connected together and their positive terminals are also connected.
In case a cell has a trouble it stops operating or operates badly. This cell should be substituted by another one.
Text 2
The principle of the starter motor is based on magnetism and it has been constructed very much like a dynamo. It has field coils, armature and brushes, but its method of operation is the reverse of that of the dynamo. The dynamo is driven by the engine and it produces current which flows to the battery. When the starter motor is operated continually and the engine will not fire, the battery is very soon exhausted.
Passing a current through a wire conductor creates a magnetic field around the conductor and again if the conductor is coiled around a soft-iron core, the magnetic field is intensified. This arrangement gives us an electromagnet as in the dynamo, but whereas in the dynamo the electromagnets are magnetized during manufacture by passing an electric current through thpm, in the starter motor current passes through them from the battery. This happens whenever the starter switch is operated and a strong magnetic field is created around them. If we can also pass the current through the armature, the armature coils will also produce a magnetic effect and will have a north and south polarity.
Слова к тексту: starter motor—пускатель электродвигателя; starter switch - пусковой переключатель.
Text 3
The atom of any elementary substance consists of a positively charged nucleus and electrons, negatively charged particles surrounding the nucleus. The electrons surrounding the atomic nucleus are located on certain energy levels or shells.
Energy may be imparted to an atom in various ways, for instance, by heating the substance or by irradiation. Depending upon the atom of energy received, an electron either becomes detached from the atom, or moves from a lower to a higher energy level, where it is not so closely bound with the nucleus. Excess energy puts the atom into an excited state, i. e. into one of the several possible higher energy states. In the excited state the atom is unstable. It returns to the normal state as a result of a spontaneous rearrangement of the electronic structure of the atom, the electrons filling free spaces in the shells closest to the nucleus.
When an electron is ejected from an atom ,the latter, having a prevailing positive charge, becomes a positively charged ion.
The ion may become neutral by attracting the nearest free electrons.
Text 4
The electric ignition system depends upon the principle of electromagnetic induction to do its work. In permanent magnets, a magnetic field exists between the north and south poles. This magnetic field consists of invisible magnetic lines of force. If we move a wire up and down in this field, the wire «cuts» the lines of force.
This action causes a small current to flow in the wire. If we reverse the procedure and pass the electric current through a wire, an electromagnetic field forms about the wire. This field can be made stronger by adding many more turns of wire and inserting a soft iron core to conduct the magnetic lines of force. A strong electromagnetic field is produced when current such as that supplied by a 6 - or 12 volt battery is passed through the wire. The soft iron core becomes a strong electric magnet. If we suddenly break this circuit, the electromagnetic field collapses and the winding around the soft iron core actually cuts the magnetic lines of force of the collapsing field. This causes a high-voltage current to be induced in the winding and a spark to jump at the gay where the wire was broken. This is the beginning of an ignition system, and is called its primary winding. The voltage produced by the system, about 250 volts, is not high enough to cause a spark to jump across the gap of a spark plug; therefore, an additional winding is added. This is called the secondary winding. It, too, cuts magnetic lines of force when we break the primary circuit and a much higher voltage is induced in it because it has many more turns of wire than the primary circuit. The voltage of the secondary circuit is 15.000 to 20.000 volts.
Text 5
The magnets used in compasses, instruments, magnetos, and all the various array of equipment which embodies a magnetic field produced by a magnet, are artificially constructed of hardened steel, magnetized by a strong magnetic flux. This type of magnet may be said to be a permanent magnet, in contrast to the electromagnet. A magnet is a body possessing the property magnetic substances.
The so-called permanent magnet should be used where a constant magnetic field is to be produced, since a well-made permanent magnet loses its magnetism very slowly, and then only up to a certain point, after which it is said to be aged. Thereafter it maintains a constant degree of magnetism unless subjected to strong de-magnetizing effects. A bar which has been magnetized is found to have poles. There are centers where magnetic attraction is strongest. If the magnet is free to turn, the pole which points notherly is called a north pole, and the other a south pole. Like poles repel each other with a magnetic force, and unlike poles attract each other. The earth is a large magnet having magnetic poles somewhere near, but not coincident with, the geographic poles.
Слова к тексту: thereafter - согласно этому; de-magnetizing- размагничивающий.