The shape of the lesson
By the end of the lesson, learners can
- Compare the two motions: Switch between a transverse and a longitudinal wave and watch how the particles move relative to the wave.
- Direction of vibration: The single difference is the direction the particles vibrate compared with the direction the wave travels.
One picture every idea returns to
In a transverse wave the vibrations are at right angles to the direction the energy travels, as in light and water waves. In a longitudinal wave the vibrations are along the direction of travel, as in sound, which travels as compressions and rarefactions.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Across, or along.. Shake a rope and the wave runs along it while the rope itself flicks up and down, across the motion. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Compare the two motions | Switch between a transverse and a longitudinal wave and watch how the particles move relative to the wave. Project tab 3 of the lab (Transverse and longitudinal) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Direction of vibration | The single difference is the direction the particles vibrate compared with the direction the wave travels. | Cooperative Concept Mapping |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (8 questions, 24 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Direction of vibration, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| In both types the particles only vibrate about a fixed point; they do not travel along with the wave. | And sound is longitudinal, not transverse, a point examiners test often. |
Transverse and longitudinal waves: worksheet
8 questions, 24 marks. Written in the style of the papers; no past paper question is reproduced.
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 waveClassify 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 stringThe 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.
The diagram shows a longitudinal wave travelling along a slinky spring to the right. Four regions are labelled A, B, C and D.
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.
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.
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 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]Answer key and marking notes
(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.
(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.
(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".
(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 is a transverse electromagnetic wave. It does not need a medium, so it can travel through a vacuum.
- Sound is a longitudinal wave. It needs particles (a medium) to pass on the compressions and rarefactions.
- Space is a vacuum, with (almost) no particles, so sound has nothing to travel through.
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.
(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) 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.
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which statement describes a transverse wave?
- AThe vibrations are at right angles to the direction in which the energy travels.
- BThe vibrations are along the direction in which the energy travels.
- CIt consists of compressions and rarefactions.
- DIt cannot travel through a vacuum.
Which of the following is a longitudinal wave?
- Aa sound wave travelling through air
- Ba light wave
- Ca radio wave
- Da ripple on the surface of water
Quiz key
In a transverse wave the vibrations are perpendicular to the direction of energy transfer. Options B and C describe a longitudinal wave; D is not generally true (light is transverse and crosses a vacuum).
Sound is a longitudinal wave: the air vibrates back and forth along the direction the sound travels. Light, radio waves and water ripples are all transverse.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.