Telephone

The world ‘tele’ means distance and phone means a sound. Thus telephone means a sound heard at a distance. It means the system by which verbal news and views are sent from one place to another through an instrument. The telephone consists of a transmitter line and a receiver. The telephone was invented in 1875 by Alexander Graham Bell. His serious of experiments made it possible to transmit sound over an outdoor line up to a distance of two miles. The perfection of the blake transmitter made possible good practical telephone transmission. Immediately, the problem arose of establishing means to connect the liens of different subscribers whenever they wished to talk. This problem was overcome in 1878 with the opening of the first central office of exchange. In 1900, the ringing by both the user and the exchange was possible whenever they wished to initiate or complete the calls. The present day telephone system provides vast improvements over those earlier designs and construction. To communicate the conversations over a greater distance. The sound waves of speech must be converted in to a from of energy that can be transmitted efficiently over many miles. The telephone system depends on electricity for its working. When a person wishes to communicate some news, he speaks into the transmitter and that is reproduced at the place through the receiver. The places between which there is a telephone connection are connected by electric wires. The essential parts of the transmitter of a telephone are the mouth piece,a thin iron diaphragm,a carbon plate ,a box filled with the granules of carbon and and cover plate . The receiver consists of a hard rubber core,a permanent magnet and a thin iron disc or diaphragm. The carbon granules of the transmitter cause vibrations in resistance in the electric circuit that varies the strength of the current in accordance with the vibrations of the diaphragm. When a rapidly changing electric current flows into the receiver ,it sets up magnetic fields around the coils . These magnetic fields alternately strengthen and weaken d the magnetic fields about the permanent magnet as the sound waves strike the transmitter. This Vibration in current strength causes the receiver diaphragm to vibrate in sympathy and so give us the sound of words. Bersides the transmitter and receiver,the telephone system includes many other components, such as ringer, switch board that help to provides satisfactory services. A telephone system which provides telephone communications within a particular local area is a telephone exchange. By inter connections telephone exchange, services can be provided between telephone stations served by two or more exchange. The transmissions lines, inter connections the control office of different exchange, are called trunk lines. There are two basic telephone system classified according to the method of switching used at the control office. These are the manual system and the dial system. The heaviest traffic is usually handled best by the dial telephone system in which the dial and automatic electro-mechanical or electrical means perform all the operations. Otherwise, the operations would have to be performed manually by an operat0r.