Waves and Wave Properties Waves
You must be able to: Describe the difference between transverse and longitudinal waves Describe evidence that waves transfer energy not matter Describe waves in terms of amplitude, wavelength, frequency and period Explain how wave speed, frequency and wavelength are linked.
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Transverse and Longitudinal Waves • • •
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There are two types of wave: transverse and longitudinal. All waves transfer energy from one place to another. For example, if a stone is dropped into a pond, ripples travel outwards carrying the energy. The water does not travel outwards (otherwise it would leave a hole in the middle). The particles that make up a wave oscillate (vibrate) about a fixed point. In doing so, they pass the energy on to the next particles, which also oscillate, and so on. The energy moves along, but the matter remains. In a transverse wave, e.g. water wave, the oscillations are perpendicular (at right-angles) to the direction of energy transfer. This can be demonstrated by moving a rope or slinky spring up and down vertically – the wave then moves horizontally. In a longitudinal wave, e.g. sound wave, the oscillations are parallel to the direction of energy transfer. This can be demonstrated by moving a slinky spring moving back and forward horizontally – the wave also moves horizontally.
Properties of Waves •
All waves have a: – frequency – the number of waves passing a fixed point per second, measured in hertz (Hz) – amplitude – the maximum displacement that any particle achieves from its undisturbed position in metres (m) – wavelength – the distance from one point on a wave to the equivalent point on the next wave in metres (m) – period – the time taken for one complete oscillation in seconds (s). Crest Amplitude
Wavelength
Key Point Waves transfer energy not matter. Transverse Waves Hand movement up and down
Direction of wave movement
Longitudinal Waves Hand movement in and out Compression Rarefaction Direction of wave movement
Undisturbed position
0
1
Time (s)
Trough Frequency = 4 waves per second
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GCSE Combined Science Revision Guide
227841 AQA Higher Tier Combined Science All-in-One_P158_187.indd 182
6/29/16 11:57 AM