Video Summary - GCSE Physics - Longitudinal & Transverse Waves - Labelling & Calculating Wave Speed (2027/28 exams)

Summary

Waves transfer energy, not matter. Light and sound carry energy from a source to a receiver. This energy can also convey information, such as images or music.
Waves travel through oscillations—repeated vibrations around an equilibrium position.

On a displacement–distance graph, distance shows how far along the wave you are, while displacement shows how far the wave has moved from its equilibrium position.
Amplitude is the maximum displacement from equilibrium.
Wavelength ((\lambda)) is the distance covered by one complete oscillation. It can be measured between matching points, such as crest to crest.
A crest is the top of a wave; a trough is the bottom.
On a displacement–time graph, one complete oscillation corresponds to the time period ((T)): the time taken for one full cycle.

Frequency ((f)) is the number of complete oscillations per second and is measured in hertz (Hz).
Use:
- (f = \frac{1}{T})
- (T = \frac{1}{f})
For example:
- If the time period is 0.5 s, the frequency is (1 \div 0.5 = 2\ \text{Hz}).
- If the frequency is 4 Hz, the time period is (1 \div 4 = 0.25\ \text{s}).

Use wave speed = frequency × wavelength, or:

[ v = f\lambda ]

Make sure the wavelength is in metres before calculating.

For example, for a wave with a frequency of 400 Hz and a wavelength of 70 cm:

In a transverse wave, oscillations are perpendicular to the direction of energy transfer. Examples include electromagnetic waves (such as light and radio waves), water ripples, and waves on a guitar string.
In a longitudinal wave, oscillations are parallel to the direction of energy transfer. This creates alternating compressed and spread-out regions. Examples include sound waves and seismic P waves.