Telephone І :


Telephone, communication instrument designed to transmit speech and other sounds to a distant point by means of electricity, and to reproduce them. The telephone contains a diaphragm, which vibrates when struck by sound waves. The vibrations (wave motion) are converted into electrical impulses and transmitted to a receiver, which converts the impulses back into sound.
In common usage, the term “telephone” is also applied in a much broader sense to the entire system to which an individual telephone set is connected; a system which allows the sending of not only a user’s voice but also data, pictures, or any other information which can somehow be encoded and converted into electrical energy. This information is exchanged between points connected to the network. The telephone network consists of all of the transmission paths between subscriber’s sets and of the switching machinery used to select a particular path or group of paths between subscribers.


II DEVELOPMENT In 1854 the French inventor Charles Bourseul suggested that vibrations caused by speaking into a flexible disc or diaphragm might be used to connect and disconnect an electric circuit, thereby producing similar vibrations in a diaphragm at another location, where the original sound would be reproduced. A few years later, the German physicist Johann Philip Reis invented an instrument that transmitted musical tones but could not reproduce speech. In 1877, having discovered that only a steady electric current could be used to transmit speech, the American inventor Alexander Graham Bell produced the first telephone capable of transmitting and receiving human speech with its quality and timbre.


III BELL’S MAGNETIC TELEPHONE The basic unit of Bell’s invention consisted of a transmitter, a receiver, and a single connecting wire. The transmitter and receiver were identical; each contained a flexible metallic diaphragm and a horseshoe magnet with a wire coil. Sound waves striking the diaphragm caused it to vibrate in the field of the magnet. This vibration generated an electric current in the coil that varied in proportion to the vibrations of the diaphragm. The current travelled through a wire to the receiving station, where it produced changes in the strength of the magnetic field of the receiver, causing its diaphragm to vibrate and reproducing the original sound.
In the receiver of the modern telephone the magnet has been flattened into the form of a watch, and the magnetic field acting on the ferrotype iron diaphragm has been made more intense and uniform. The modern transmitter consists of a thin diaphragm mounted behind a perforated grill. At the centre of the diaphragm is a small dome forming an enclosure filled with carbon granules. Sound waves passing through the grill cause the dome to move in and out. When the diaphragm presses in, the granules become densely packed, allowing an increase in the flow of current through the transmitter ... .


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