Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall and use both the equations below for all waves: wave speed…
Full specification wording
Topic 4 – Waves: 4.6 Recall and use both the equations below for all waves: wave speed (metre/second, m/s) = frequency (hertz, Hz) × wavelength (metre, m); wave speed (metre/second, m/s) = distance (metre, m) ÷ time (second, s)
Both equations describe the same wave speed, so choose the one that matches the data given.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 6 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
Both equations describe the same wave speed, so choose the one that matches the data given. When frequency and wavelength are supplied, multiply them: a wave of frequency 50 Hz and wavelength 4 m travels at 50 × 4 = 200 m/s. When a wave travels a measured distance in a measured time, divide distance by time: 340 m in 2 s gives 340 ÷ 2 = 170 m/s. Keep units consistent — hertz means cycles per second, wavelength must be in metres, and time in seconds. Rearranging matters too: wavelength = speed ÷ frequency, and time = distance ÷ speed. Check that the answer's unit is m/s and that the size is sensible for the wave described.
What earns the marks
- Selects the equation linking speed, frequency and wavelength when frequency and wavelength are given.
- Multiplies frequency in hertz by wavelength in metres to obtain wave speed in m/s.
- Selects the distance-over-time equation when a travelled distance and time are given.
- Divides distance in metres by time in seconds to obtain wave speed in m/s.
- Rearranges either equation correctly to find frequency, wavelength, distance or time.
- Keeps units consistent, converting centimetres to metres or milliseconds to seconds before calculating.
Common mistakes and how to put them right
Adds frequency and wavelength instead of multiplying them.
Put it right: Multiply the two quantities to find speed.
Divides wavelength by frequency rather than speed by frequency.
Put it right: Rearrange so wavelength = speed ÷ frequency.
Leaves a wavelength in centimetres while using metres per second.
Put it right: Convert to metres first.
Uses the distance–time equation when only frequency and wavelength are supplied.
Put it right: Match the equation to the data given.
Exam tips
- Write down the equation, then substitute values with their units before calculating.
- Check the unit of your answer is m/s and that its size is reasonable for the wave.
- If a value is in centimetres or milliseconds, convert to metres or seconds first.
Try the lesson
The start of the Topic 4 – Waves: 4.6 Recall and use both the equations below for all waves: wave speed (metre/second, m/s) = frequency (hertz, Hz) × wavelength (metre, m); wave speed (metre/second, m/s) = distance (metre, m) ÷ time (second, s) lesson, made from checked teaching notes for this specification point.
Have a go first
A wave has a frequency of 20 Hz and a wavelength of 3 m. What is its wave speed?
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Test your understanding of Topic 4 – Waves: 4.6 Recall and use both the equations below for all waves: wave speed (metre/second, m/s) = frequency (hertz, Hz) × wavelength (metre, m); wave speed (metre/second, m/s) = distance (metre, m) ÷ time (second, s)
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