Eight original Cambridge-style questions. Three of them ask you to read a diagram, the skill examiners test most often on this topic. Attempt each in your notebook, then reveal the worked solution.
The single most useful habit for this topic: before classifying any wave, find the direction of energy transfer and the direction the particles move. If they are at right angles, it is transverse. If they are along the same line, it is longitudinal. Everything else follows from that one comparison.
Define what is meant by each of the following, in terms of the direction in which the particles oscillate.
(a) a transverse wave (b) a longitudinal wave(a) Transverse: the particles oscillate perpendicular (at right angles) to the direction of energy transfer. ✓
(b) Longitudinal: the particles oscillate parallel to (along the same line as) the direction of energy transfer. ✓
The phrase "direction of energy transfer" is what earns the mark. Saying "the way the wave goes" is too vague for the examiner.
Classify each of the following waves as either transverse or longitudinal.
(a) light (b) sound in air (c) water surface waves (d) ultrasound (e) microwaves (f) a wave on a guitar string(a) light → transverse
(b) sound in air → longitudinal
(c) water surface waves → transverse
(d) ultrasound → longitudinal (it is just high-frequency sound)
(e) microwaves → transverse (an EM wave)
(f) guitar string → transverse
Shortcut: everything on the electromagnetic spectrum is transverse. Anything that is "sound" of any frequency (including ultrasound) is longitudinal.
The diagram shows a transverse wave travelling along a rope. The wave is moving to the right. Point P is a single point on the rope.
(a) To the right (horizontally), as shown by the arrow. ✓
(b) Up and down (vertically), at right angles to the wave direction. ✓
(c) Crest ✓
Point P does not move along the rope. It only moves up and down about its rest position. This is the heart of "energy travels, matter does not".
The diagram shows a longitudinal wave travelling along a slinky spring to the right. Four regions are labelled A, B, C and D.
(a) Compressions (coils bunched together): A and C ✓
(b) Rarefactions (coils spread apart): B and D ✓
(c) Longitudinal wave. Example: sound (or ultrasound). ✓✓
Compression = squashed together = high pressure. Rarefaction = stretched apart = low pressure. The coils only move back and forth a little; the pattern of compressions travels along.
Light from the Sun reaches the Earth across the vacuum of space, but sound produced by the Sun never reaches us.
Explain this difference, with reference to the nature of the two types of wave.
Three marks, three ideas: light needs no medium, sound needs a medium, space has no medium. Hit all three.
The two diagrams below each show the direction of energy transfer (green arrow) and the direction a single particle oscillates (black double arrow). Classify each wave as transverse or longitudinal.
Wave 1: particle moves at right angles to energy → transverse ✓
Wave 2: particle moves along the same line as energy → longitudinal ✓
This is the whole topic in one picture. Compare the two arrows. Perpendicular = transverse. Parallel = longitudinal.
During an earthquake, two types of seismic wave travel through the Earth. P-waves are longitudinal and S-waves are transverse.
(a) In a P-wave, how do the rock particles move relative to the direction the wave travels? [1] (b) S-waves cannot pass through the liquid outer core, but P-waves can. Suggest why a longitudinal wave can travel through a liquid while a transverse wave cannot. [2](a) Parallel to the direction of travel: the particles move back and forth along the wave direction. ✓
(b) A longitudinal wave passes energy by squashing and stretching the material (compressions), which a liquid can do. A transverse wave needs the material to be dragged sideways and spring back, but a liquid cannot resist this sideways shearing, so it cannot carry a transverse wave. ✓✓
A "suggest" question rewards sensible reasoning even on unfamiliar ground. The key idea: liquids can be compressed but cannot resist being sheared sideways.
A student is comparing a sound wave travelling through air with a beam of light travelling through air.
(a) State the type of wave each one is. [2] (b) For each wave, state the direction the oscillation occurs relative to the direction of energy transfer. [1] (c) State which of the two waves could still travel if all the air were removed, and explain why. [1](a) Sound → longitudinal. Light → transverse. ✓✓
(b) Sound: oscillation parallel to energy transfer. Light: oscillation perpendicular to energy transfer. ✓
(c) Light would still travel, because it is an electromagnetic wave and needs no medium. Sound would stop, because it needs particles to travel through. ✓
A clean compare question. Keep your two waves clearly separated in your answer so the examiner can award each mark without hunting.