The World Communicates
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Communications and Waves
Communication is the transfer of information. This cannot take place without the transfer of energy. Many of today's communications systems transfer information and energy using waves.

A wave may be represented by a graph that shows displacement against either distance or time.

Amplitude is the maximum displacement of the wave.

The crest of the wave is the point of maximum positive displacement and the trough is the point of maximum negative displacement.

The distance between two crests (or troughs) on a displacement vs distance graph is the wavelength l.

The time between two crests (or troughs) on a displacement vs time graph is the period T of the wave.

For a wave travelling through space, the number of crests that pass a fixed point in one second is the wave's frequency f in hertz (Hz).

Period and frequency are related by:      f = 1 / T

The wave's frequency f in Hz and wavelength l in metres are related to its velocity v in metres/sec according to ...
If the wave's displacement is parallel to its velocity it is called a longitudinal wave. Sound travelling through air is a longitudinal wave.

If the wave's displacement is perpendicular to its velocity it is called a transverse wave. Light is a transverse wave.

You will find some interesting applets that illustrate wave action at http://www.surendranath.org/Applets.html

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