IGCSE Physics / Properties of waves
Transverse and longitudinal waves revision notes
Edexcel International GCSE Physics (4PH1), chapter 10: Properties of waves, specification point 3.2, 3.4, 3.1. Free lesson.
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Waves transfer energy and information from place to place without transferring matter. The direction of the oscillations compared with the direction of energy transfer tells you whether a wave is transverse or longitudinal.
What a wave transfers
A wave carries energy and information from one place to another, but it does not carry matter with it. The particles in the material only oscillate, meaning they move backwards and forwards about one position. This is like a crowd doing a Mexican wave: the wave moves round the stadium, but each person stays in their seat. The material a wave passes through does not travel along with the wave.
How a transverse wave moves
In a transverse wave, the oscillations are at right angles to the direction the energy travels. For example, a wave can travel along a rope to the right while each point on the rope moves up and down. The rope moves about its own position rather than travelling with the wave. A full repeat of the wave shape is one wavelength, measured in metres (m). The height of a crest above the middle position is the amplitude. Frequency is measured in hertz (Hz), and wave speed is measured in metres per second (m/s). Examples include light and other electromagnetic waves, water waves, and…
How a longitudinal wave moves
In a longitudinal wave, the oscillations are parallel to the direction the energy travels. In a slinky, the coils move backwards and forwards along the same line as the wave. The coils still oscillate about their own positions rather than travelling along with the wave. A compression is a bunched-up part of the wave. A rarefaction is a spread-out part. One wavelength is the distance from one compression to the next. Amplitude is how far a particle moves from its rest position. Sound, including sound in air, is a longitudinal wave.
How to compare the two types
The key difference is the direction of the oscillations compared with the direction of energy transfer. Transverse waves have crests and troughs, while longitudinal waves have compressions and rarefactions. Transverse: oscillations at right angles to the direction of energy transfer. Longitudinal: oscillations parallel to the direction of energy transfer. Electromagnetic waves can travel through a vacuum, which is empty space. Sound cannot, because it needs particles to pass the vibrations on.
How to describe the difference for marks
A clear comparison describes both types of wave. The word “perpendicular” means at right angles, but it is too vague on its own. Name the oscillations and state their direction compared with the direction of energy transfer.