| English | Wavelength |
|---|---|
| Bahasa Melayu | Panjang gelombang |
| 中文 | 波长 |
Definition
The distance between two successive points in phase on a wave, such as two neighbouring crests; measured in metres (m).
In exam terms
Wavelength is the distance between two successive points that are in phase, for example between two neighbouring crests or two neighbouring compressions. Its symbol is the Greek letter λ (lambda) and it is measured in metres (m).
Wavelength links to speed and frequency through the wave equation v = fλ, where v is in m s⁻¹, f in Hz and λ in m. For example, a wave of frequency 50 Hz travelling at 20 m s⁻¹ has wavelength λ = v ÷ f = 20 m s⁻¹ ÷ 50 Hz = 0.4 m.
On a displacement-distance graph the wavelength is the horizontal length of one complete cycle.
Do not confuse it with period
Wavelength is a distance along the wave (metres), while period is a time for one cycle (seconds). Both describe one complete wave, so students mix them up.
The clue is the axis: read wavelength from a displacement-distance graph and period from a displacement-time graph.
In Paper 2 you may be asked to define wavelength, or to determine it from a graph or from v = fλ. Always state metres as the unit, and measure from one point to the next identical point, not to the halfway point.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)