GCSE Physics - Longitudinal & Transverse Waves - Labelling & Calculating Wave Speed (2026/27 exams)

Waves transfer energy from one place to another without transferring matter. Examples include light waves from a phone screen and sound waves from speakers, both of which transfer energy that our brains interpret as information.

Waves oscillate to travel. A displacement-distance graph shows displacement (how far the wave oscillates from equilibrium) and distance (how far the wave has traveled). Key terms include amplitude (maximum displacement), wavelength (distance of one complete oscillation), crest (top of a wave), and trough (bottom of a wave).

A displacement-time graph shows time on the x-axis, making the length of one complete oscillation the time period. The time period is the time taken for one complete oscillation. Frequency, measured in hertz, is the number of complete oscillations per second and can be calculated as 1 divided by the time period (F = 1/T).

Wave speed can be calculated by multiplying the wavelength by the frequency (Wave Speed = Wavelength × Frequency). For example, a sound wave with a frequency of 400 Hz and a wavelength of 70 cm (0.7 m) would have a wave speed of 280 m/s.

In transverse waves, oscillations are perpendicular to the direction of energy transfer. This means the vibrations are up and down while the wave moves left to right. Examples include electromagnetic waves (light, radio), water ripples, and waves on guitar strings.

Longitudinal waves have oscillations parallel to the direction of energy transfer, leading to regions of compression (more dense) and rarefaction (more spread out). Sound waves and seismic P-waves are examples of longitudinal waves.