How do you use the wave equation v = fλ?
Short answer
Wave speed = frequency × wavelength, written v = fλ. Speed is in metres per second (m/s), frequency in hertz (Hz) and wavelength in metres (m). If the frequency increases while the speed stays the same, the wavelength must decrease.
Step by step
- Identify the values: frequency in Hz, wavelength in m.
- Convert units: kHz to Hz (× 1000), cm to m (÷ 100).
- Use v = fλ, or rearrange: f = v ÷ λ, λ = v ÷ f.
- Give the answer with units.
Worked example
A sound wave has a frequency of 680 Hz and a speed of 340 m/s. Find its wavelength.
- λ = v ÷ f
- λ = 340 ÷ 680
- λ = 0.5 m
Common mistakes
- Leaving wavelength in centimetres.
- Confusing frequency with period. Period T = 1 ÷ f.
- Thinking frequency changes when a wave enters a new medium. The speed and wavelength change; frequency stays the same.
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