Physics GCSE: Uses of Waves

Information carrying

Types of signals

A rapidly increasing amount of people own mobile phones and there are very few houses in the U.K. that do not have some form of telecommunication. In the past all the systems were based on analogue signals but now the world is going digital.

Analogue signals

Analogue signals cover a whole continuous range of values.

Digital signals 

Digital signals have only two values off (0) and on (1).

Digital signals have two main advantages:

• They are a higher quality than analogue signals. This is because they are not changed as much as analogue signals when they are transmitted. (Transmitted means moved or transferred from one point to another.)
• More information can be sent as a digital signal, in a certain length of time, compared with analogue signals.

When signals are transmitted they lose energy so signals are amplified to increase the energy again. Signals can also pick up extra, unwanted signals. This is called noise.

For analogue signals the different frequencies in the signal lose different amounts of energy. When the signal is amplified these differences and any noise are also amplified. This makes the signal deteriorate and become less and less like the original signal.

This problem is less noticeable with digital signals, as the on and off states are easy to see, even with some noise added. The quality of the signal is less affected by the transmission. 

Optical fibres versus copper cables 

When telecommunications began signals were sent from house to house along copper cables, via switchboards. Now optical fibres have replaced many of these copper cables.

Electrical signals have to be used in copper cables, whereas electromagnetic waves can be used in optical fibres. By using digital signals, information can be sent along the optical fibres as pulses of light.

There are three main advantages of using optical fibres rather than coppercables:

• Optical fibres allow much faster transmission (delivery) of the signals than copper cables.
• Optical fibres can also carry far more information than a copper cable that is the same diameter.
• Light pulses lose less energy as they travel along an optical fibre than an electrical signal in a copper cable.

Changing waves into electrical signals 

Waves have energy. This energy can be changed into other forms. For instance, when electromagnetic waves are absorbed by metal, the energy that is absorbed can be changed into an electrical signal as an alternating current. Match the correct devices to the wave form changes below.

Sound waves can also be converted to electrical signals, using a microphone. This is how speech and music can be transmitted long distances along cables. The electrical signals can then be converted to electromagnetic waves that can be sent along optical fibres or to satellites.

If waves are converted to electrical signals so that the frequency and amplitude of the electrical signal match the frequency and amplitude of the wave being converted, the electrical signal is an analogue signal. This signal can then be converted to a digital signal.