How does a telephone work?

Despite the fact that you can conference call people on the other side of the world on the phone, the telephone actually works along quite simple principles. Interestingly, the technology behind the phone in your home has not really changed over the past century. You could take a phone from the 1930s, plug it into the phone jack in your hall or living room and it would still work. So, How does a telephone work?

Inside the mouthpiece on the handset is a thin metal coating. Between this and an electrode is a thin barrier – these days it is made of plastic. This barrier is connected to a wire that carries the electric current.

When you speak into the mouthpiece, you create acoustic vibrations. This moves the metallic coating a little nearer to the electrode, which in turn creates voltage variations. This converts the acoustic energy into electrical energy.

These electrical pulses are carried along the wire to the speaker on the receiving end. The electric pulses are then turned back into acoustic energy – so you hear the voice on the other end of the phone. In a very simple phone, you would hear your own voice through the speaker, which would be rather annoying to say the least, so most phones feature something called a duplex coil, which stops the sound of your voice from getting back to your own ear!

So why do you need to convert the acoustic energy into electrical pulses? Well, electrical energy travels at the speed of light and as it travels along well-insulated wires, little of the energy is dispersed as it goes along. If you decided to send acoustic pulses along a metal pipe, for instance, the pipe would absorb the acoustic energy before it reached its desired destination.

So along with the speaker and microphone, the simplest phone only has one other core component – a hook switch that connects and disconnects the phone to and from the network. When you lift up the receiver, the hook switch connects you and then disconnects when you put down the receiver.

So how is your phone connected to the wider network? There is a pair of copper wires running from one box in the road to another box at your home. The wires are connected to each of the phone jacks in your house. The box in the road is connected to thick cable that consists of more than 100 pairs of copper wires, which run to another box that acts as a digital concentrate and then on to the phone company’s exchange, where it connects to the wider network.

Depending on where you are calling when you pick up your phone, the phone company either forms a loop between your own phone and the handset of the person you are calling, or, if it a long-distance call, it digitizes your voice (along with the voices of thousands of other callers!) and sends it on a long-distance network – it may go along a fiber-optic line – or even be sent via satellite.