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What are the features of a wave, and how are wave speed, frequency and wavelength related?

Transverse and longitudinal waves, the features of a wave (amplitude, wavelength, frequency, period), and the wave equation.

A focused answer to the WJEC GCSE Science Double Award Unit 3 topic on waves, covering transverse and longitudinal waves, the features amplitude, wavelength, frequency and period, and the wave equation linking speed, frequency and wavelength.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. Transverse and longitudinal waves
  3. The features of a wave
  4. The wave equation
  5. Frequency and period
  6. Sound as a longitudinal wave
  7. Measuring waves on an oscilloscope
  8. Try this

What this dot point is asking

WJEC Double Award Unit 3 wants you to distinguish transverse and longitudinal waves, describe the features of a wave, and use the wave equation.

Transverse and longitudinal waves

All waves transfer energy from one place to another without transferring matter: the water in a ripple moves up and down but does not travel along with the wave.

The features of a wave

A bigger amplitude means more energy (a louder sound or brighter light); a higher frequency means more waves per second (a higher-pitched sound).

The wave equation

To use it, pick the form you need, substitute the values in the correct units, and work out the answer.

Frequency and period

The frequency and period are linked: T=1fT = \dfrac{1}{f}. A wave with a frequency of 5 Hz has a period of 15=0.2 s\dfrac{1}{5} = 0.2\,\text{s}, meaning each wave takes 0.2 seconds. A higher frequency means a shorter period. This relationship is useful when a question gives the time for one wave instead of the frequency.

Sound as a longitudinal wave

Sound is a good example of a longitudinal wave. The particles of the air vibrate back and forth along the direction the sound travels, creating compressions (where particles are squashed together) and rarefactions (where they are spread out). Because sound needs particles to vibrate, it cannot travel through a vacuum, which is why there is no sound in space. The pitch of a sound depends on its frequency (higher frequency means higher pitch) and the loudness depends on its amplitude (bigger amplitude means louder). Linking these everyday properties to the features of the wave is a common exam point.

Measuring waves on an oscilloscope

Waves such as sound can be displayed on an oscilloscope, which shows the wave as a trace on a screen. The height of the trace shows the amplitude, and the distance between peaks (with the time setting) lets you work out the period and then the frequency using f=1Tf = \dfrac{1}{T}. A taller trace means a louder sound; peaks closer together mean a higher frequency and a higher pitch. Being able to read amplitude and period from an oscilloscope trace, and use them to find the frequency, is a common practical skill.

Try this

Q1. State the unit of frequency. [1 mark]

  • Cue. The hertz (Hz).

Q2. A wave has frequency 10 Hz and wavelength 3 m. Calculate its speed. [2 marks]

  • Cue. v=fλ=10×3=30 m/sv = f\lambda = 10 \times 3 = 30\,\text{m/s}.

Exam-style practice questions

Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

WJEC style3 marksA wave has a frequency of 50 Hz and a wavelength of 6 m. Calculate its speed.
Show worked answer →

A Unit 3 calculation. Use the wave equation v=fλv = f\lambda (1 mark). Substitute f=50 Hzf = 50\,\text{Hz} and λ=6 m\lambda = 6\,\text{m}: v=50×6v = 50 \times 6 (1 mark) =300 m/s= 300\,\text{m/s} (1 mark). Markers reward the equation, the substitution and the unit metres per second. A common error is to divide instead of multiply.

WJEC style4 marksDescribe the difference between a transverse and a longitudinal wave, giving an example of each.
Show worked answer →

A Unit 3 describe question worth 4 marks. Reward: in a transverse wave the vibrations are at right angles (perpendicular) to the direction the wave travels (1), for example light or water waves (1); in a longitudinal wave the vibrations are along (parallel to) the direction the wave travels, as compressions and rarefactions (1), for example sound (1). Markers credit the direction of vibration and an example for each. A common error is to swap the two or to give the wrong example.

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