The term “electric current” is used to mean electricity which flows through a conductor, a direct current being a current which flows in one direction only. There are four principal ways by which a direct current can be generated, viz.
1) chemical action;
2) thermal or heat action, the word thermal, coming from the Greek word “therme” which means “heat”;
3) light action;
4) magnetic action.
To set up a current by chemical action, an alkali or an acid is used to react with a metal. Such an apparatus is called an electric cell, a group of two or more cells connected together forming a battery.
To produce a current by thermal action, heat is applied to two unlike metals soldered together in two places, the apparatus of this kind being called a thermoelectric couple or thermocouple, for short. We get the prefix “thermo” from “thermal”, the origin of the last word having been mentioned above. The word “couple” in this term means that two unlike metals or metals and alloys are joined together so that they can be properly heated in the point of the joint.
The reason the thermocouple generates a current is due to the fact that the heat tears the electrons off of the negative inetal at the junction, just as the chemical action of an electric cell tears the electrons off of the zinc electrode. It is these electrons that form the current flowing through the circuit.
To develop a current by light action, light is made to fall on a special kind of a cell, the apparatus to be used in such a case being called a photoelectric cell.
Finally, in order to generate a current, a wire is made to cut, that is, to pass through a magnetic field, this latter being set up either by a permanent magnet or an electromagnet. Where the wire cuts through the magnetic field of a permanent magnet, the apparatus is called a magneto-electric machine or just “magneto”, for short. The wire cutting through the magnetic field of an electromagnet, the apparatus is called a dynamo electric machine, or “dynamo”, for short.
In general there are a number of ways by which electric currents can be generated by magnetic action, all of them being based on the same principle, that of cutting the magnetic lines of force with a conductor.
III. Упражнения на все случаи употребления форм, оканчивающихся на –ing:
A
1. Having overcome the economic backwardness inherited from the tsarist Russia, the Soviet Union increased its output of means of production 83-fold, as compared to 1913. 2. The sufferings of people under German fascists were terrible. 3. In America about one million hectares of valuable farm land have been confiscated for military testing ground and camps and every day brings fresh reports of peasant farms being converted to the same purpose and of whole villages being torn down to make room for military installations. 4. The growing economic difficulties are prompting the average American to lift his voice for peace and international cooperation.
1. The disintegration of radioactive substances is a spontaneous process, no method accelerating or retarding it being known. 2. Carbon dioxide may be obtained by heating some carbonates to a high temperature. 3. In chemical changes occurring in substances atoms continue to be indivisible. 4. Water vapour can be condensed into a liquid by taking away heat or by decreasing its volume. 5. Sometimes the cooling without the increasing of pressure results in liquefying the gas. 6. While teaching mathematics Tsiolkovsky continued his self-education studying astronomy, biology, and chemistry. 7. Stanyukovich distinguished himself as a gifted writer, most of his novels being connected with the sea.
B
1. The Soviet national budget is an important medium for raising living standards of the people. 2. Peaceful cooperation among nations espousing different social system is both possible and desirable. 3. Taking advantage of the suddenness of their treacherous attack, the German-fascists strove to crush our army by powerful blows at the beginning of the war. 4. The lifting of the blockade of Leningrad was a great success of both our land and naval forces. 5. The Japanese yoke having been removed by the Soviet Army, the people of North Korea saw their way to independence, democracy, and progress.
1. The temperature having been raised, the vapour began forming again. 2. Having added an alkaline solution, we got a dark precipitate at the bottom of the vessel. 3. Having been evaporated, the solution of the mother liquid of calcium chloride gave white precipitate. 4. When testing the properties of the gas evolved while heating mercuric oxide, we find that it is pure oxygen. 5. The air being shut off the fire, combustion stops. 6. Shipbuilding and fishing industries are widely developed in this part of the country.
C
1.The USSR consistently continues its policy for the safe-guarding of security and for the promoting of peace and friendship among all nations. 2. By safeguarding respect for their sovereignty, by opposing foreign interference in the conduct of their affairs, by refusing to allow the establishing of military bases and any form of occupation by foreign troops, the peoples can guarantee their security and protection of peace. 3. Atlantic block is being torn by deep contradictions. 4. French soldiers demonstrated against being sent to North Africa for suppressing the liberation movement there.
1. At the age of 20 Tsiolkovsky began teaching; a profession at which he continued working for 40 years. 2. The splitting of atom liberates great quantities of energy. 3. Atomic energy is the foundation of all processes occurring in our universe. 4. Yellow sand having been used in manufacture, the glass had a yellowish color. 5. The atomic explosion is based on the splitting of the atom. 6. Two bodies being placed in contact with each other, the temperature of the hot body falls while the temperature of the cold body rises. 7. The current in a circuit is decreased when the resistance is increased, other factors remaining the same.
IV. Переведите текст; выделите все формы, оканчивающиеся на –ing и определите их функции:
ELASTICITY
Pulling a rubber band increases its length. However, if you cease pulling it and release one of its ends, the rubber band will quickly return to its original shape and size.
Solids in greatly differing degrees resist being changed in shape, i.e. resist deformation. Some of them, like a rubber band or a steel spring, are called elastic because they return to their original size and shape after having been stretched or compressed. Others are known as elastic because they straighten after having been bent.
Gases and liquids are perfectly elastic. In spite of them having been compressed they return to their original volume after the removing of the applied force.
Air, for instance, is perfectly elastic. If it is compressed and then allowed to return to its original pressure and temperature, it returns exactly to its original volume.
We may define an elastic body as one tending to return to its original shape and size when the deforming force is removed. On the contrary, bodies that are not very elastic do not show the tendency of returning to their original form. Thus, elasticity is the tendency to return to the original condition after deformation.
Careful experiments made on various elastic materials show that there is a simple relationship existing between the acting force and the resistance force. This relationship must have a limit somewhere and the stretching cannot be increased indefinitely.
Elastic limit is the point beyond which one should not attempt deforming the body if it is to return to its original condition.
As we are stretching an elastic object such as a steel spring, for instance, there must come a time when the elastic limit is reached, and then the above-mentioned relationship will not hold any longer. However, stretching the steel spring repeatedly or leaving it stretched moderately has no practical effect upon it. Considering further the example of the rubber band, one finds that the more the rubber band is pulled, the longer it will become until the elastic limit is reached, at last. It is known, however, that rubber can stretch a relatively long distance before reaching the elastic limit.
