Classical Wave Theory
All waves, whatever type they are, carry energy.
Waves come in two type: longitudinal and transverse.
1. In a longitudinal wave, the wave moves in the same direction as the energy.
2. In transverse waves, the wave moves ‘sideways’ whilst it moves energy along.
Sound waves are longitudinal.
Water waves, light waves and radio waves are all transverse waves.
The video below gives a summary of both transverse and longitudinal waves.
The top of a wave is the crest or peak.
The bottom of a wave is the trough.
The distance between crests is called the Wavelength (λ), usually measured in metres.
The height of a wave from the centre to the crest is called the amplitude (A), usually measured in metres.
The bigger the Amplitude, the more Energy the wave carries. Loud sounds have a bigger Amplitude than quiet sounds.
The frequency (f) of a wave is the number of waves per second. It is measured in Hertz (Hz).
The period (T) of a wave is the length of time a single wave takes to pass. The higher the frequency (waves coming more often) the smaller the period.
When a wave passes through a gap or over a barrier, it diffracts – it changes direction.
Small gaps (about the size of the Wavelength) cause lots of diffraction. Large gaps cause less diffraction.
The longer the Wavelength, the more the wave diffracts.
Sound waves have a long Wavelength – they diffract around edges so we can hear people around the corner. Light waves have a very short Wavelength. They hardly diffract at all, so we can’t see people around corners. Radio waves have a long wavelength, so they can diffract enough to reach houses behind hills.TV waves are much shorter wavelength, so they don’t diffract as much. Houses behind hills may not be able to pick up TV signals.
When light travels from one material (like air) into another (like glass), it slows down. This usually causes the light to change direction.
The change in speed of the light is called refraction. Different materials slow light down by different amounts.