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How the telephone works

The telephone combined the knowledge of how sound works together with a variable electric signal that could be sent over great distances.

Instead of the telegraph's simple electrical pulse - on or off - the telephone uses an electrical signal that changes in amplitude (volume) and frequency (pitch) across time - in other words, a 'continuously varying signal'.

This is more like real life, and means that the telephone is able to carry a human voice. But for the scientists of the day it required a better understanding of electricity as well as technological progress in the areas of cables and switches.

Sound

Sound : good vibrations

The sound waves that you hear are quite simply movements or vibrations of air. These sound waves travel through air, like the wind, by changes in air pressure.

Different sounds come about because the air vibrates at different frequencies. And as the trailer for the film 'Alien' made clear - 'in space, no-one can hear you scream ...' - sound can't travel in a vacuum because there's no air.

The substance that a sound wave travels through is called its 'transmission medium'. Sound waves can, in fact, travel through almost any medium, such as water or the bricks in your house, and in many cases much further than in air. Whale songs can travel for hundreds of miles underwater, although you'd need special equipment to listen to them if you were more than about 10 miles away.

How does an electromagnet work? : the basics made simple

How does an electromagnet work? : the basics made simple

Inside the telephone : which part does what?

Inside the telephone : which part does what?

How does a carbon microphone work? : the basics made simple

How does a carbon microphone work? : the basics made simple

How does a telephone earpiece work? : the basics made simple

How does a telephone earpiece work? : the basics made simple

Dial : it all clicks into place

Dial : it all clicks into place
fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

what's on

The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

featured story

100 years of automatic switching!
In 1912 the GPO installed Britain's first automatic telephone exchange in Epsom.

Discover the early days of the telephone...