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II. Read and translate the text.When a cell or any other generator is connected and forms a continuous path of conductors, the electrons begin to move through conductors. This is called an electric current, an electric circuit. We know that current is the flow of electricity through a circuit. If broken anywhere, the electric circuit will stop carrying a current. There are two main types of current: direct and alternating. When electrons flow in one direction only, the current is called a direct current. When electrons flow first in one direction and then in another in a periodic manner, the current is called an alternating current. An alternating current is a current that changes its direction of flow through a circuit in a periodic manner. Alternating current flows in cycles. The number of cycles per second is termed the frequency of current. In a 60-cycle alternating current circuit, the current flows in one direction 60 times per second and in the other direction 60 times per second. Two frequencies are in use nowadays: the standard for Europe is 50 cycles per second, while the standard for the USA is 60 cycles per second. A standard frequency has a great advantage since different electrical systems can be interconnected.
Vocabulary III. Remember these words:
Grammar IV. Translate into English: standard frequency; advantages of standard frequency; regular overload; disadvantages of regular overload; control elements; electric field; under test. V. Translate the following sentences and define the functions of the word provided. 1. Current starts flowing provided a voltage source is applied to the circuit. 2. The new equipment can be utilized provided a protection fuse is applied to it. 3. These electrical devices can work for a long time provided they are made of high quality material. 4. These electrical devices are provided with rubber insulators. 5. These electrical devices provided with rubber insulators were produced at a large factory. VI. Test. Choose the correct variant: 1. Direct current … a) changes its direction of flow; b) flows in one direction. 2. Alternating current flows provided… a) a direct voltage source is applied; b) an alternating voltage source is applied. 3. The frequency of the circuit is … a) the number of cycles per minute; b) the number of cycles per second. 4. A standard frequency has … a) great advantages; b) disadvantages. 5. Different systems can be in interconnected… a) due to various frequencies; b) due to the standard frequency. Speaking VII. Answer the following words: 1. What is current? 2. What is circuit? 3. What types of current do you know? 4. What type is termed a direct current (an alternating current)? 5. What is frequency?
Date: 2015-12-11; view: 1978
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