3.3.1.2
Longitudinal waves oscillate parallel to the direction of travel
Wave Types, Polarisation & Stationary Waves — AQA A-Level Physics
Key Definition
Longitudinal wave — A wave in which the particles oscillate parallel to the direction of the wave travel and energy transfer.
- Longitudinal waves show regions of compressions (increased pressureForce per unit area. Measured in pascals (Pa), where 1 Pa = 1 N m⁻².) and rarefactions (decreased pressureForce per unit area. Measured in pascals (Pa), where 1 Pa = 1 N m⁻².).
- Examples: sound waves, ultrasoundSound waves with frequencies above 20 kHz (beyond human hearing). Medical ultrasound typically uses 1-15 MHz. waves, waves through a slinky coil, seismic P-waves.
- Longitudinal waves cannot be polarised.
- One wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m). is the distance between two consecutive compressions or two consecutive rarefactions.
Examiner Tips and Tricks
- The definitions of transverse and longitudinal waves are frequently asked in exams.
- Learn both by heart.
- The key word is the direction of oscillation relative to the direction of wave travel: perpendicular for transverse, parallel for longitudinal.