| English | Longitudinal wave |
|---|---|
| Bahasa Melayu | Gelombang membujur |
| 中文 | 纵波 |
Definition
A wave in which the particles of the medium vibrate parallel to the direction the wave travels, such as sound waves.
In exam terms
A longitudinal wave is a wave in which the particles of the medium vibrate parallel to (along the same line as) the direction in which the wave travels. It is made of compressions (regions where the particles are pushed close together, at high pressure) and rarefactions (regions where they are spread apart, at low pressure).
The main example is a sound wave.
Like any wave, its speed is v = fλ, where v is in m s⁻¹, f in hertz (Hz) and λ in metres (m). Example of correct use: sound is a longitudinal wave, so it needs a medium and cannot travel through a vacuum.
Do not confuse it with…
Do not confuse a longitudinal wave with a transverse wave. In a longitudinal wave the particles vibrate parallel to the direction of travel, forming compressions and rarefactions; in a transverse wave they vibrate at right angles to it, forming crests and troughs.
On a displacement graph a compression matches a crest and a rarefaction matches a trough.
In Paper 2 this is usually asked as state what is meant by a longitudinal wave or name a longitudinal wave. The expected answer gives the direction of vibration relative to the direction of travel and names sound as the example.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)