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An alternating current, or power, transformer is made on the same principle as a spark coil, that is, it has a soft iron core, a primary coil formed of a couple of layers of heavy wire, and a secondary coil wound up of a large number of turns of very fine wire.
Furnaces of an altogether different type are those employing an alternating current, such as the Kjellin and Rochling furnaces, where the metal to be heated really forms the secondary circuit of a large and novel form of transformer which in principle is analogous to the familiar transformer seen to step down the potential of alternating current as for house lighting.
When the current from the battery flows through the primary coil it magnetizes the soft iron core and as the microphone varies the strength of the current the high voltage alternating currents set up in the secondary coil of the induction coil are likewise varied, when they are impressed upon and modulate the oscillating currents. The Microphone Transformer.
Unlike the spark coil, however, which has an open magnetic core and whose secondary coil is wound on the primary coil, the transformer has a closed magnetic core, with the primary coil wound on one of the legs of the core and the secondary wound on the other leg. It has neither a vibrator nor a condenser.
Tesla has also shown that vacuum bulbs can be lit inside without any outside connection with the current, by means of an apparatus like that shown in figure 70, where D is an alternating dynamo, C a condenser, P S the primary and secondary coils of a sparking transformer, T T two metal sheets or plates, and SB the exhausted bulbs.
When sounds vibrate the ribbon extremely low alternating voltages are developed at the ends of the ribbon, which has a very low impedance of only 0.15 ohm, necessitating the use of a step-up transformer of 1:45 turns ratio very close to it. The frequency response is 20 to 16,000 Hz.
How Receiving Set No. 2 Works. When the electric oscillations that are set up by the incoming electric waves on the aerial wire surge through the primary coil of the oscillation transformer they produce a magnetic field and as the lines of force of the latter cut the secondary coil, oscillations of the same frequency are set up in it.
To use the amplified radio frequency oscillating currents or amplified audio frequency alternating currents that are set up by an amplifier tube either a high resistance, called a grid leak, or an amplifying transformer, with or without an iron core, must be connected with the plate circuit of the first amplifier tube and the grid circuit of the next amplifier tube or detector tube, or with the wire point of a crystal detector.
For here we have not only the dynamo, motors, and transformers that he gave freely to the world, not only the alternating-current transformer, and the system of transmission of power, but we even find that the principal consumers of the enormous electric power produced are employing it in carrying on some of the many processes in electro-chemistry, a science that he had done so much to advance.
Without it high pressure would be impossible and it is on high pressure that success of long distance transmission depends. To convey electricity to distant centres at a low pressure would require thousands of dollars in copper cables alone as conductors. To illustrate the service of the transformer in electricity it is only necessary to consider water power at a low pressure.
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