working of telephone?

The telephone was created through the cross-pollination of two fields of study - electricity and acoustics. Although the invention of the telephone is usually credited to Alexander Graham Bell, many inventors were working on the problem throughout the 1860s and 1870s, most notably Elisha Gray, who filed a patent application for the same device only a few hours after Bell did. Although the basics of electricity were known by the 1830s, nobody suggested transmitting speech electrically until 1854. The telephone was finally invented on March 10, 1876. Into it were spoken the famous words, "Mr. Watson, come here, I want to see you."

The telephone operates on simple principles. A telephone mouthpiece contains a thin metallic coating separated from an electrode by a thin barrier (today we use plastic) which connects to a wire carrying an electric current. When a person speaks into the mouthpiece, the acoustic vibrations from her speech push the metallic coating slightly closer to the electrode, resulting in variations in voltage and therefore a speedy conversion from acoustic to electric energy. The electric pulses are conveyed through a wire to the speaker on the other end, where electric pulses are converted into acoustic energy again.

Converting speech to electrical energy before transmission is far more efficient than conveying speech through a mechanical channel, for example a metal pipe, because the walls of mechanical channels absorb so much of the acoustic energy as it travels. Well-insulated wires, however, are effective at protecting electrical energy from dispersing before reaching its destination. Electrical pulses travel at the speed of light, whereas acoustic pulses are limited by the speed of sound. In his 1627 book New Utopia, Francis Bacon referred to the possibility of a long-distance network of tubes to transmit human speech. Many historians consider this the first reference to something like a telephone. Unfortunately, he lacked the scientific knowledge to understand why this would be impractical.