Edexcel GCSE Physics Topic 4 Waves: a complete overview of wave properties, transverse and longitudinal waves, the wave speed equation, measuring wave speed and behaviour at boundaries

What Topic 4 actually demands

Waves is a Paper 1 topic that mixes precise vocabulary, a key calculation (the wave speed equation), a core practical, and conceptual explanation of wave behaviour at boundaries. It also sets up Topic 5 on light and the electromagnetic spectrum, so a firm grasp here pays off later.

This guide walks through all five dot points of the topic, then sets out the exam patterns Pearson repeats. Each dot point has a matching page with practice questions; this overview ties them together.

Wave properties

A wave transfers energy and information without transferring matter. The key terms are amplitude (maximum displacement from rest), wavelength (distance between corresponding points on adjacent waves), frequency (waves per second, in $\text{Hz}$), period ($T = \frac{1}{f}$), wave velocity, and wavefront. The duck-on-a-pond example shows energy transfer without matter transfer.

Transverse and longitudinal waves

In a transverse wave the oscillations are perpendicular to the direction of energy transfer (electromagnetic and water waves). In a longitudinal wave they are parallel (sound waves), with compressions (particles close together) and rarefactions (particles spread apart). All electromagnetic waves are transverse; sound is longitudinal and cannot travel through a vacuum.

The wave speed equation

The wave speed equation has two forms: $v = f \times \lambda$ and $v = \frac{x}{t}$. Rearrange to $f = \frac{v}{\lambda}$ or $\lambda = \frac{v}{f}$. Keep wavelength in metres and frequency in hertz. All electromagnetic waves travel at the same speed in a vacuum, so a higher frequency means a shorter wavelength.

Measuring wave speed

The core practical measures wave speed in a solid and a fluid. The speed of sound is found with two microphones and an oscilloscope or by an echo method (doubling the wall distance). Ripples are measured in a ripple tank, finding the frequency by counting waves and the wavelength across several waves. Measuring several wavelengths and repeating reduces error.

Behaviour at boundaries

At a boundary a wave may be reflected, transmitted (and refracted if it changes speed), or absorbed. Refraction is the change of direction caused by a change of speed when a wave crosses a boundary at an angle: towards the normal into a slower medium, away from the normal into a faster one. The wavefronts pivot because one side changes speed first.

How Topic 4 is examined

A typical Edexcel profile for Waves:

• Definitions. Amplitude, wavelength, frequency and period, with strict wording.
• Calculations. The wave speed equation in all three rearrangements, often combined with the distance-time form.
• Core practical. Describing how to measure the speed of sound or water ripples and the equation used.
• Boundary behaviour. Naming reflection, refraction, transmission and absorption, and explaining refraction with wavefronts.

Check your knowledge

A mix of recall and calculation questions covering Topic 4. Attempt them under timed conditions, then check against the solutions.

1. Define the amplitude of a wave. (1 mark)
2. State what a wave transfers without transferring matter. (1 mark)
3. State the difference between a transverse and a longitudinal wave. (2 marks)
4. A wave has a frequency of $25\,\text{Hz}$ and a wavelength of $4\,\text{m}$. Calculate its speed. (2 marks)
5. A wave travels at $30\,\text{m/s}$ with a wavelength of $6\,\text{m}$. Calculate its frequency. (2 marks)
6. Name the regions of high and low pressure in a sound wave. (2 marks)
7. Name three things that can happen to a wave at a boundary. (3 marks)
8. State which way light bends when it enters glass from air at an angle. (1 mark)