OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Describe and apply the relationship between wavelength, frequency and wave…
Full specification wording
Wave behaviour: describe and apply the relationship between wavelength, frequency and wave velocity
Wavelength, frequency and wave velocity are linked by one relationship: velocity equals frequency multiplied by wavelength (v = f × λ).
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 4 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Wavelength, frequency and wave velocity are linked by one relationship: velocity equals frequency multiplied by wavelength (v = f × λ). Wavelength λ is the distance between two matching points on consecutive waves, measured in metres; frequency f is the number of complete waves passing a point each second, measured in hertz (Hz), where 1 Hz = 1 s⁻¹. Multiplying hertz by metres gives metres per second, so the units confirm the equation. A wave of frequency 50 Hz and wavelength 4 m travels at 50 × 4 = 200 m/s. For a fixed velocity, increasing frequency shortens wavelength and decreasing frequency lengthens it, because f and λ are inversely proportional when v is constant. Describe the relationship in words, then apply it by substituting two known quantities to find the third, rearranging to f = v ÷ λ or λ = v ÷ f as needed.
What earns the marks
- States that wave velocity equals frequency multiplied by wavelength, written v = f × λ.
- Identifies wavelength as the distance between matching points on successive waves, measured in metres.
- Identifies frequency as the number of waves passing a point each second, measured in hertz.
- Rearranges the relationship to find frequency as velocity divided by wavelength or wavelength as velocity divided by frequency.
- Explains that for a constant velocity a higher frequency gives a shorter wavelength and a lower frequency gives a longer wavelength.
- Substitutes two known values into the relationship and calculates the third with correct units, for example 50 Hz × 4 m = 200 m/s.
Common mistakes and how to put them right
Adds frequency and wavelength instead of multiplying them.
Put it right: Multiply the two quantities to obtain velocity.
Divides wavelength by frequency when finding velocity.
Put it right: Multiply frequency by wavelength instead.
Treats hertz as a unit of wavelength.
Put it right: Record frequency in hertz and wavelength in metres.
Forgets to rearrange before substituting when finding frequency or wavelength.
Put it right: Divide velocity by the known quantity.
Exam tips
- Write the equation v = f × λ before substituting so the rearrangement is clear.
- Check units: hertz multiplied by metres must give metres per second.
- Use the inverse relationship to sanity-check an answer: a larger frequency should pair with a smaller wavelength at fixed velocity.
Try the lesson
The start of the Wave behaviour: describe and apply the relationship between wavelength, frequency and wave velocity lesson, made from checked teaching notes for this specification point.
Have a go first
A water wave has a frequency of 4 Hz and a wavelength of 3 m. What is the velocity of the wave?
Listen
Wavelength, frequency and wave velocity are linked by one relationship: velocity equals frequency multiplied by wavelength (v = f × λ). Wavelength λ is the distance between two matching points on consecutive waves, measured in metres; frequency f is the number of complete waves passing a point each second, measured in hertz (Hz), where 1 Hz = 1 s⁻¹. Multiplying hertz by metres gives metres per second, so the units confirm the equation. A wave of frequency 50 Hz and wavelength 4 m travels at 50 × 4 = 200 m/s. For a fixed velocity, increasing frequency shortens wavelength and decreasing frequency lengthens it, because f and λ are inversely proportional when v is constant. Describe the relationship in words, then apply it by substituting two known quantities to find the third, rearranging to f = v ÷ λ or λ = v ÷ f as needed. A strong answer earns marks for these points. States that wave velocity equals frequency multiplied by wavelength, written v = f × λ. Identifies wavelength as the distance between matching points on successive waves, measured in metres. Identifies frequency as the number of waves passing a point each second, measured in hertz. Rearranges the relationship to find frequency as velocity divided by wavelength or wavelength as velocity divided by frequency. Exam tip: Write the equation v = f × λ before substituting so the rearrangement is clear.
See it
Key words
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Wave velocity
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Wavelength
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Frequency
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Inverse relationship
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See every definition
- Wave velocity
- Equals frequency multiplied by wavelength, written v = f × λ, and is found by multiplying the two quantities.
- Wavelength
- The distance between two matching points on consecutive waves, measured in metres.
- Frequency
- The number of complete waves passing a point each second, measured in hertz (Hz), where 1 Hz = 1 s⁻¹.
- Inverse relationship
- For a fixed velocity, increasing frequency shortens wavelength and decreasing frequency lengthens it, because f and λ are inversely proportional when v is constant.
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