Lesson 13. Topic “Generators’. Grammar material ...（13课。）.pdfVIP

Lesson 13. Topic “Generators’. Grammar material: Prepositions. Text: “Generators” The dynamo invented by Faraday in 1831 is certainly a primitive apparatus compared with the powerful, highly efficient generators and alternators that are in use today. Nevertheless, these machines operate on the same principle as the one invented by the great English scientist. When asked what use his new invention had, Faraday asked in his turn; What is the use of a new-born child? As a matter of fact, the new-born child soon became an irreplaceable device we cannot do without. Although used to operate certain devices requiring small currents for their operation, batteries and cells are likely to supply light, heat and power on a large scale, indeed, we need electricity to light up millions of lamps, to run trains, to lift things, and to drive the machines. Batteries could not supply electricity enough to, do all this work. That dynamo-electric machines are-used for this purpose is a well-known fact. These are the machines by means of which mechanical energy is turned directly into electrical energy with a loss of only a few per cent. It is calculated that they produce more than 99.99 per cent of all the worlds electric power. There are two types of dynamos, namely, the generator and the alternator. The former supplies d.c. which is similar to the current from a battery and the latter, as its name implies provides a.c. To generate electricity both of them must be continuously provided with energy from some outside source of mechanical energy such as steam engines, steam turbines or water turbines, for example. Both generators and alternators consist of the following principal parts: an armature and an electromagnet. The electromagnet of a d.c. generator is usually called a stat