Howstuffworks "How Telephones Work"

Although most of us take it completely for granted, the telephone you have in your house is one of the most amazing 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 just 100 years ago, when it might have taken several weeks to get a one-way written message to someone, you realize just how amazing the telephone is!

animated image of how a telephone network works

This illustration shows the entire telephone network, including a home connection, cell phone towers, long distance exchanges and transcontinental connections. Click here to see the animated version!

In this article, we will look at the telephone device that you have in your house as well as the telephone network it connects to so you can make and receive calls.

A Simple Telephone
Surprisingly, a telephone is one of the simplest devices you have in your house. 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 work fine!

The very simplest working telephone would look like this inside:

As you can see, it only contains three parts and they are all simple:

A switch to connect and disconnect the phone from the network - This switch is generally called the hook switch. It connects when you lift the handset.
A speaker - This is generally a little 50-cent, 8-ohm speaker of some sort.
A microphone - In the past, telephone microphones have been as simple as carbon granules compressed between two thin metal plates. Sound waves from your voice compress and decompress the granules, changing the resistance of the granules and modulating the current flowing through the microphone.

That's it! You can dial this simple phone by rapidly tapping the hook switch -- all telephone switches still recognize "pulse dialing." If you pick the phone up and rapidly tap the switch hook four times, the phone company's switch will understand that you have dialed a "4."