What waves do
- Waves transfer energy from one place to another without transferring matter.
- For ripples on water and sound waves in air, it is the wave that travels, not the water or air itself. A floating object only bobs up and down as a ripple passes.
Transverse waves
- In a transverse wave, the oscillations (vibrations) are perpendicular (at right angles) to the direction of energy transfer.
- Examples: ripples on the surface of water, waves on a string, and all electromagnetic waves, such as light.
- Transverse waves have peaks (crests) and troughs.
Longitudinal waves
- In a longitudinal wave, the oscillations are parallel to the direction of energy transfer.
- They have areas of compression (particles close together) and rarefaction (particles spread out).
- Example: sound waves travelling through air. Seismic P-waves are also longitudinal.
Describing waves
- Amplitude: the maximum displacement of a point on a wave away from its undisturbed position.
- Wavelength (λ): the distance from a point on one wave to the equivalent point on the next wave, for example peak to peak.
- Frequency (f): the number of waves passing a point each second, measured in hertz (Hz).
- Period (T): the time for one complete wave to pass a point. T = 1 ÷ f.
Key terms
- Wave
- A way of transferring energy without transferring matter.
- Transverse wave
- A wave whose oscillations are perpendicular to the direction of energy transfer.
- Longitudinal wave
- A wave whose oscillations are parallel to the direction of energy transfer.
- Compression
- A region of a longitudinal wave where the particles are close together.
- Rarefaction
- A region of a longitudinal wave where the particles are spread out.
- Amplitude
- The maximum displacement of a point on a wave from its undisturbed position.
- Wavelength
- The distance from one point on a wave to the same point on the next wave.
- Frequency
- The number of waves passing a point each second, in hertz.
- Period
- The time taken for one complete wave to pass a point.