C.2.1—Transverse and longitudinal travelling waves

Feature	Transverse wave	Longitudinal wave
Oscillation direction	perpendicular to propagation	parallel to propagation
Snapshot features	crests and troughs	compressions and rarefactions
Mechanical example	wave on a stretched rope	sound in air

Follow one particle, not the drawn shape

At a fixed position, a medium particle oscillates with time about equilibrium. In a position snapshot, different particles have different displacements at the same instant. The travelling pattern and energy move through the medium; the particles do not travel with the pattern.

Classification rule

Compare the particle or field oscillation direction with the propagation direction. A sinusoidal-looking graph alone does not determine whether a wave is transverse or longitudinal.

How it is assessed

Questions ask you to define a travelling wave or infer point motion and wave direction from a transverse snapshot. The evidence rewards separate statements for energy transfer, local oscillation and propagation.

Command terms

Outline / What is

What earns marks

Define a travelling wave as propagation of energy through oscillations or fields, then distinguish the direction of particle motion from the direction of wave travel. For a diagram, use the stated motion of one point to infer the next point and the propagation direction.

Watch for

Confusing the direction of a point’s oscillation with the direction in which the wave and energy propagate.

Representative question

[Maximum number: 2]

Outline what is meant by a travelling wave.

Model the transfer

A travelling wave propagates a disturbance and transfers energy without a resultant transport of the medium. Use the local particle/field motion to describe oscillation, and the wave direction to describe propagation.

Connect the quantities

Describe waves with wavelength $\lambda$ , frequency $f$ , period $T$ , amplitude and speed $v$ , linked by $v=f\lambda=\lambda/T$ . Measure wavelength between adjacent in-phase points.

Classify the wave

Transverse oscillations are perpendicular to propagation; longitudinal oscillations are parallel. Mechanical waves require a medium, while electromagnetic waves are transverse field oscillations and travel at $c$ in vacuum.

Final check

At a boundary, identify which quantity is fixed by the source and which properties change in the new medium. Keep units consistent and distinguish propagation speed from the local oscillation speed.

C.2.1—Transverse and longitudinal travelling waves

Distinguish Transverse and Longitudinal Travelling Waves

C.2.1 Exam Analysis

Assessment in practice

Retrieve the C.2 Wave Model

Question 1