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What are the features of waves, and how are wave speed, frequency and wavelength linked?

Transverse and longitudinal waves, amplitude, wavelength, frequency and period, and the wave equation linking speed, frequency and wavelength.

A focused answer to WJEC GCSE Physics topic 1.5 on the features of waves, covering transverse and longitudinal waves, amplitude, wavelength, frequency and period, the period-frequency relationship, and the wave equation linking speed, frequency and wavelength.

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  1. What this topic is asking
  2. Transverse and longitudinal waves
  3. The key wave quantities
  4. Frequency and period
  5. The wave equation
  6. Try this

What this topic is asking

WJEC wants you to distinguish transverse and longitudinal waves, define the key wave quantities, and use the wave equation. This is part of topic 1.5 Features of waves in Unit 1 of WJEC GCSE Physics (3420).

Transverse and longitudinal waves

In both kinds, the particles vibrate about a fixed position and pass energy on to their neighbours; they do not travel along with the wave.

The key wave quantities

Frequency and period

The wave equation

You can investigate waves using a ripple tank for water waves or a vibrating string, measuring the wavelength and frequency to find the speed. In a ripple tank a small motor dips into water at a set frequency and a lamp projects the wave pattern onto a screen below; measuring the distance across several wavelengths and dividing by the number of waves gives a more accurate wavelength than measuring a single one. On a stretched string fixed at both ends, a vibration generator produces standing waves whose wavelength can be measured directly, and changing the frequency or the tension changes the pattern. These practicals are good ways to check that v=fλv = f\lambda holds and to practise reducing measurement error by averaging over many waves.

Try this

Q1. A wave has a period of 0.25 s0.25\,\text{s}. Calculate its frequency. [2 marks]

  • Cue. f=1T=10.25=4.0 Hzf = \dfrac{1}{T} = \dfrac{1}{0.25} = 4.0\,\text{Hz}.

Q2. State what is meant by the amplitude of a wave. [1 mark]

  • Cue. The maximum displacement of a point from its rest position.

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 20193 marksA water wave has a frequency of 4.0 Hz4.0\,\text{Hz} and a wavelength of 0.50 m0.50\,\text{m}. Calculate its speed.
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A topic 1.5 Calculate question on the wave equation v=fλv = f\lambda. State the values: frequency f=4.0 Hzf = 4.0\,\text{Hz} and wavelength λ=0.50 m\lambda = 0.50\,\text{m} (1 mark for selecting the equation). Substitute: v=fλ=4.0×0.50=2.0 m/sv = f\lambda = 4.0 \times 0.50 = 2.0\,\text{m/s} (2 marks for the calculation and the unit metres per second). Markers reward the equation, the substitution and the unit. A common error is to divide rather than multiply, or to forget the unit.

WJEC 20224 marksDescribe the difference between a transverse and a longitudinal wave, giving one example of each.
Show worked answer →

A topic 1.5 Describe question. In a transverse wave the oscillations are at right angles (perpendicular) to the direction the wave travels (1 mark), for example a wave on a water surface or any electromagnetic wave such as light (1 mark). In a longitudinal wave the oscillations are along (parallel to) the direction of travel, producing compressions and rarefactions (1 mark), for example a sound wave (1 mark). Markers reward the perpendicular versus parallel oscillation and a valid example of each. A common error is to swap the two definitions.

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