As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. It is important to note that the amplitude is not the distance between the top and bottom of a wave.
The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the trough of one wave to the crest of the next wave. But it doesn't matter where you measure it - as long as it is the same point on each wave.
The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second.
The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies. For example:
- most people cannot hear a high-pitched sound above 20 kHz
- radio stations broadcast radio waves with frequencies of about 100 MHz
- most wireless computer networks operate at 2.4 GHz
When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is diffraction.
The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap.