Saturday, 4 November 2017

Struggle of Alexander Graham Bell


What is a telephone?

A telephone is a device used for communication over long distance. It converts sound, especially the human voice, into electronic signal that are transmitted over lon distances via cables or other transmission media. Since its invention, the telephone has been greatly improved an many variants of the original prototype have been developed to serve the various need of people. Today, telephone are indispensable to businesses, government, offices and households.

When was the telephone invented                      and by whom?

The telephone was first patented in 1876 by Alexander Graham Bell, though its invention was the culmination of work done by many individuals, simultaneously. Bell wanted to improve the telegraph, a wire based electrical system that had been an established means of communication. The telegraph was basically limited to receiving and sending one message at a time. Bell designed a 'harmonic telegraph', which was based on the principal that several notes could be sent simultaneously along the same wire, if the notes or signal differed in pitch.
All that he needed was a working transmitter with a membrane capable of varying electronic currents and a receiver that would reproduce these variation in audible frequencies. While experimenting with his harmonic telegraph, Bell discovered he could hear sound over a wire. The sound was that of a twanging clock spring. Thus the idea of the telephone was realized. Bell's first design had a single - port that required the user to alternately speak into and then listen through the same hole.

What are the part of a telephone?

The handset of a telephone consist of a microphone (transmitter) to speak into and an earphone (receiver)  which reproduces the voice of the distant person. The dial may be located either on the handset, or on a base unit to which the handset is connected by cord containing wires. The base unit also contains an alerting device, called the ringer, and a switch hook , which is spring - loaded button that gets pressed, when the handset is put on base units. The switch hook actually breaks the electrical circuit thus terminating the call. There is also a duplex coil that blocks the caller's voice from reaching his ear.

 How does a telephone work?

A telephone's mouthpiece that contain a transmitter has a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound wave strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds,depending on the variations in air pressure caused by the varying tones of the speaker's voice. Behind the diaphragm lies a small cup filled with tiny grains of carbon which, which contain a low voltage electric current. Louder sound create stronger vibrations that squeeze the carbon grains more loosely. As the vibrating diaphragm presses against these carbon grains, the current copies the pattern of the sound waves and travels over a telephones wire to the receiver of another telephone. The receiver also a diaphragm with two magnets - a permanent magnet that constantly holds the diaphragm close to it stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker's speech pattern. As the diaphragm moves in and out, it the same as the ones sent into the transmitter. The sound wave strike the ear of the listener and he hears the words of the speaker.

How many types of telephones are            there?

Telephone are made in variety of form. A landline telephone is connected by a pair of wires to the telephone network, while a mobile phone communicates through radio transmission. A cordless telephone has a portable handset base station which is connected by a wire to the telephone network.
A satellites telephone or satphone is a type of mobile phone that connects to orbiting satellites, instead of terrestrial cell sites.

what is the structure of a telephone network ?

The telephone network consists of a worldwide net of telephone line, fibre optic cable, microwave transmission, cellular network, communications satellites, and undersea telephones cable connected by switching centers.