AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Properties of waves: v = f λ
This equation links the speed of a wave to its frequency and wavelength.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 11 of 18
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This equation links the speed of a wave to its frequency and wavelength. Speed v is measured in metres per second (m/s), frequency f in hertz (Hz) and wavelength λ in metres (m). Frequency is the number of complete waves passing a point each second, while wavelength is the distance from one point on a wave to the same point on the next wave, such as crest to crest. Rearranging gives f = v ÷ λ and λ = v ÷ f. For example, a sound wave of frequency 250 Hz travelling at 340 m/s has wavelength 340 ÷ 250 = 1.36 m. The equation applies to all waves, including sound, light, water and seismic waves, provided consistent units are used.
What earns the marks
- State that v represents wave speed in metres per second (m/s), f represents frequency in hertz (Hz) and λ represents wavelength in metres (m).
- Recognise that frequency is the number of complete waves per second and wavelength is the distance between equivalent points on consecutive waves.
- Substitute known values into v = f λ correctly, converting units such as cm to m or kHz to Hz before calculating.
- Rearrange the equation to find frequency using f = v ÷ λ or wavelength using λ = v ÷ f when those quantities are required.
- Interpret a calculated wavelength or frequency in context, for example judging whether a value is sensible for a sound or light wave.
Common mistakes and how to put them right
Using wavelength in centimetres while speed is in m/s, which gives an incorrect answer.
Put it right: Convert all lengths to metres before substituting.
Confusing frequency with time period.
Put it right: Frequency is in Hz and period is in seconds, with f = 1 ÷ T.
Multiplying frequency by wavelength when trying to find frequency.
Put it right: Rearrange to f = v ÷ λ instead of using v = f λ directly.
Exam tips
- Write the equation, substitute values with units, then calculate and give the unit in your final answer.
- Check whether the question asks for speed, frequency or wavelength before rearranging, as this determines which form of the equation to use.
- Convert prefixes such as kHz to Hz (× 1000) and cm to m (÷ 100) before doing any arithmetic.
Try the lesson
The start of the Properties of waves: v = f λ lesson, made from checked teaching notes for this specification point.
Have a go first
A sound wave has a frequency of 50 Hz and a wavelength of 4 m. Using v = f λ, what is the speed of the wave?
Listen
This equation links the speed of a wave to its frequency and wavelength. Speed v is measured in metres per second (m/s), frequency f in hertz (Hz) and wavelength λ in metres (m). Frequency is the number of complete waves passing a point each second, while wavelength is the distance from one point on a wave to the same point on the next wave, such as crest to crest. Rearranging gives f = v ÷ λ and λ = v ÷ f. For example, a sound wave of frequency 250 Hz travelling at 340 m/s has wavelength 340 ÷ 250 = 1.36 m. The equation applies to all waves, including sound, light, water and seismic waves, provided consistent units are used. A strong answer earns marks for these points. State that v represents wave speed in metres per second (m/s), f represents frequency in hertz (Hz) and λ represents wavelength in metres (m). Recognise that frequency is the number of complete waves per second and wavelength is the distance between equivalent points on consecutive waves. Substitute known values into v = f λ correctly, converting units such as cm to m or kHz to Hz before calculating. Rearrange the equation to find frequency using f = v ÷ λ or wavelength using λ = v ÷ f when those quantities are required. Exam tip: Write the equation, substitute values with units, then calculate and give the unit in your final answer.
See it
Key words
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Frequency
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Wavelength
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Wave speed
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v = f λ
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See every definition
- Frequency
- The number of complete waves passing a point each second, measured in hertz (Hz).
- Wavelength
- The distance from one point on a wave to the same point on the next wave, such as crest to crest, measured in metres (m).
- Wave speed
- The speed v of a wave, measured in metres per second (m/s), linked to frequency and wavelength by v = f λ.
- v = f λ
- The equation linking the speed of a wave to its frequency and wavelength, applying to all waves provided consistent units are used.
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