Ciencia


Bell's Telephone

On March 10, 1876, in Boston, Massachusetts, Alexander Graham Bell invented the telephone. Thomas Watson fashioned the device itself; a crude thing made of a wooden stand, a funnel, a cup of acid, and some copper wire. But these simple parts and the equally simple first telephone call -- "Mr. Watson, come here, I want you!" -- belie a complicated past. Bell filed hisapplication just hours before his competitor, Elisha Gray, filed notice to soon patent a telephone himself. What's more, though neither man had actually built a working telephone, Bell made his telephone operate three weeks later using ideas outlined in Gray's Notice of Invention, methods Bell did not propose in his own patent.

The word “telephone” comes from the Greek words tele, meaning from afarand phone, meaning voice or voiced sound. Generally, a telephone is any device that conveys sound over a distance. A string telephone, a megaphone, or a speaking tube might be considered telephonic instruments but for our purposes they are not telephones. These transmit sound mechanically and not electrically.

How It Works

Speech is sound in motion. Talking produces acoustic pressure.Speaking into the can of a string telephone, for example, makes the line vibrate, causing sound waves to travel from one end of the stretched line to the other. A telephone by comparison, reproduces sound by electrical means. What the Victorians called "talking by lightning”.

A standard dictionary defines the telephone as "an apparatus for reproducing sound, especially that of the voice, at a greatdistance, by means of electricity; consisting of transmitting and receiving instruments connected by a line or wire which conveys the electric current." Electricity operates the telephone and your voice varies that current.

What sound waves look like

Telephone Basics

Most of us take the telephone completely for granted not realizing the telephone you have in your house is one of the mostamazing devices ever created. If you want to talk to someone, all you have to do is pick up the phone and dial a few digits. You are instantly connected to that person and you can have a two-way conversation. The telephone network extends worldwide, so you can reach nearly anyone on the planet. When you compare that to the state of the world 100 years ago, when it might have taken several weeks toget a one-way written message to someone, you realize just how amazing the telephone is!

Surprisingly, the telephone is one of the simplest devices you have in your home today. It is so simple because the telephone connection to your house has not changed in nearly a century. If you have an antique phone from the 1920s, you could connect it to the wall jack in your house and it would workfine!

The very simplest working telephone would look like the picture below on the inside. As you can see, it only contains three parts and they are all simple - click on the names of the three parts below to see more:

The Modern Phone

The only problem with the phone shown in the previous page is that when you talk, you will hear your voice through the speaker. Most people find thatannoying, so any "real" phone contains a device called a duplex coil or something functionally equivalent to block the sound of your own voice from reaching your ear. A modern telephone also includes a bell so it can ring and a touch-tone keypad and frequency generator. A "real" phone looks like the one on the right. Still, it's a pretty simple device. In a modern phone there is an electronic microphone,amplifier and circuit to replace the carbon granules and loading coil. And the mechanical bell is replaced by a speaker and a circuit to generate a pleasant ringing tone.

The Telephone Network

The telephone network starts in your house. Two pairs of copper wire run from a box (pedestal) at the road to a box (often called an entrance bridge or demarc) at your house.

From there, the two...