In simple terms
A friendly intro before the formal notes — no formulas yet.
Waves: Energy in Motion
Waves are nature's way of carrying energy from one place to another without physically moving the material itself. Think of them as energy messengers. We'll explore two main types: those that wiggle sideways (transverse) and those that push and pull forwards (longitudinal).
Imagine a crowd doing 'the wave' at a stadium. The wave of motion travels around, but the people (particles) themselves just move up and down, returning to their original spots. Similarly, when you drop a pebble in a pond, ripples spread out, carrying energy, but the water itself just bobs up and down; it doesn't flow outwards with the ripple.
- 1
Identify Oscillation: Check if particles move perpendicular or parallel to energy flow.
- 2
Spot Examples: Match specific waves (light, sound) to their type.
- 3
Measure Key Features: Understand wavelength, frequency, and period from graphs.
- 4
Test for Polarisation: If a wave can be polarised, it MUST be transverse.
What this topic covers
The official Cambridge syllabus points this lesson works through.
- 7.2.1
Compare transverse and longitudinal waves
- 7.2.2
Analyse and interpret graphical representations of transverse and longitudinal waves
Explore the concept
Use the live diagram, PhET or GeoGebra sim, and synced steps — play it, drag controls, or tap a step.
Step-synced diagram — highlights what to look for in the simulation above.
Step 1
Identify Oscillation: Check if particles move perpendicular or parallel to energy flow.
15 more simulations for this topic — run them in the Simulations section below
Simulations
Every simulation here runs the real model — try the steps on a card, then check what you see against the notes.
15 simulations · 5 to start with
Start herein this order — each one shows a different piece of the topic
- PhETStart here · 19702 7.2 · IB C.2
Sound Waves
Watch pressure fronts leave a speaker; move a listener and show the pressure graph.
Why this one: Show the graph: each compression lines up with a pressure peak, turning a longitudinal wave into a trace.
Try this
- Show “Graph” — the compressions in the picture line up with the peaks on the trace.
- Change the frequency and watch the spacing of the fronts (λ) change.
- On “Two Sources”, move the listener through loud and quiet spots.
Look for Longitudinal: particles move along the direction of travel; compressions ↔ pressure peaks.
Simulation by PhET Interactive Simulations, University of Colorado Boulder · Licensed to MarkScheme (public licence CC BY-NC 4.0 since 2026-03-30)
- The Physics ClassroomStart here · 29702 7.2 · 9702 7.1 · IB C.2
The Particle Wave
Sixty particles connected by springs; vibrate the first one at a regular rate and explore the wave that results
Why this one: Sixty linked particles: each oscillates in place while the disturbance travels along the chain.
Try this
- Vibrate the first particle and watch the disturbance spread.
- Change the rate and compare the wavelength.
- Follow one particle's motion.
Look for Each particle oscillates about a fixed position while the wave pattern moves along the chain.
Physics Interactives by The Physics Classroom · Licensed to MarkScheme (site terms otherwise permit linking only)
- PhETStart here · 39702 7.2
Wave on a String
A transverse wave you can freeze — watch one point of the string move.
Why this one: Send one pulse and watch the green bead move only up and down: transverse means perpendicular.
Try this
- Send a single pulse and watch the green bead — it moves up and down only.
- Set “Oscillate” and pause: pick two beads a whole λ apart and compare their motion.
Look for Transverse: displacement perpendicular to the direction of energy transfer.
Simulation by PhET Interactive Simulations, University of Colorado Boulder · Licensed to MarkScheme (public licence CC BY-NC 4.0 since 2026-03-30)
- The Physics ClassroomStart here · 49702 7.1 · 9702 7.2 · IB C.2
Slinky Lab
Wiggle a particle on a string; change the wiggle frequency, the amplitude and the damping and watch the disturbance travel
Why this one: Wiggle faster and the wavelength shortens at the same wave speed.
Try this
- Wiggle slowly and read the wavelength.
- Wiggle faster and compare the wavelength.
- Add damping and watch the amplitude along the string.
Look for A higher frequency gives a shorter wavelength at the same wave speed.
Physics Interactives by The Physics Classroom · Licensed to MarkScheme (site terms otherwise permit linking only)
- SimuPhysicsStart here · 59702 7.2 · IB C.2
Wave Types in a Spring
Transverse and longitudinal waves run along the same spring so the particle motions can be compared directly
Why this one: The same coil moves sideways in a transverse wave and back-and-forth in a longitudinal one.
Try this
- Run the transverse wave and watch a coil.
- Run the longitudinal wave and watch the same coil.
- Compare the direction of motion in each.
Look for Transverse coils move at right angles to the wave direction and longitudinal coils move along it.
Open on SimuPhysicsRuns on their siteSimuPhysics by Mohamed Abdelsalam · Licensed to MarkScheme (site publishes no licence; served with frame-ancestors self)
More simulations10 more on this topic — core ones first
- oPhysicsCore9702 7.1 · 9702 7.2 · IB C.2
Waves Basics & Types of Waves
Tutorial page (GIF animations, no applet): definitions of wave, medium, transverse vs longitudinal
Try this
- Read the definitions of wave and medium.
- Compare the transverse and longitudinal animations.
Look for A wave transfers energy without transferring the medium; particles oscillate across or along the direction of travel.
Open on oPhysicsRuns on their siteSimulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 7.2 · 9702 8.1 · IB C.2
Longitudinal Waves
Longitudinal travelling or standing wave; adjust speed and amplitude; see compressions and rarefactions
Try this
- Run the travelling wave and follow one compression.
- Increase the amplitude and look at the compressions.
- Switch to the standing wave and find the particles that never move.
Look for Particles oscillate along the direction of travel; compressions move at the wave speed while each particle stays near its rest position.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- oPhysicsCore9702 8.1 · 9702 7.2 · IB C.4
Air Column Resonance with Longitudinal Waves
Air-column resonance shown with longitudinal particle displacement and pressure representations
Try this
- Switch between the displacement and pressure representations.
- Find the displacement node at the closed end.
- Compare the pressure at an open end.
Look for A displacement node is a pressure antinode, so the closed end has the largest pressure variation and the open end none.
Simulation by Tom Walsh, oPhysics.com — made with GeoGebra · Licensed to MarkScheme (site: free for non-profit educational use; applets made with GeoGebra)
- SimuPhysicsCore9702 7.1 · 9702 7.2 · IB C.2
Wave Motion Simulation
Choose transverse or longitudinal, set the frequency and amplitude, and watch the wave carry energy without carrying the medium
Try this
- Choose transverse and follow one particle.
- Switch to longitudinal and follow a particle.
- Raise the frequency and compare the wavelength.
Look for Particles oscillate about fixed positions while the wave moves along.
Open on SimuPhysicsRuns on their siteSimuPhysics by Mohamed Abdelsalam · Licensed to MarkScheme (site publishes no licence; served with frame-ancestors self)
- SimuPhysicsCore9702 7.2 · IB C.2
Longitudinal Wave
Individual particles are tracked so you can see them oscillating in place while the compressions move along
Try this
- Follow one particle through a cycle.
- Follow one compression along the wave.
- Measure the distance between compressions.
Look for Particles move back and forth along the direction the wave travels.
Open on SimuPhysicsRuns on their siteSimuPhysics by Mohamed Abdelsalam · Licensed to MarkScheme (site publishes no licence; served with frame-ancestors self)
- SimuPhysicsCore9702 7.2 · IB C.2
Sound Wave Simulation
Air molecules bunch and spread while the pressure trace a microphone would record is drawn; change the frequency and amplitude
Try this
- Raise the frequency and watch the pressure trace.
- Raise the amplitude and compare.
- Match a compression with the pressure peak.
Look for Frequency sets the pitch and amplitude sets the loudness.
Open on SimuPhysicsRuns on their siteSimuPhysics by Mohamed Abdelsalam · Licensed to MarkScheme (site publishes no licence; served with frame-ancestors self)
Key formulas
Tap any symbol to reveal exactly what it means and its units.
Tap a symbol — great for exam definitions
Tap a symbol — great for exam definitions
Tap a symbol — great for exam definitions
At a glance — side by side
Compare key properties side by side — ideal for exam contrasts.
Compare transverse and longitudinal waves at a glance — a favourite exam contrast.
| Property | Transverse | Longitudinal |
|---|---|---|
| Direction of particle oscillation | Perpendicular to energy flow | Parallel to energy flow |
| Can be polarised? | Yes | No |
| Examples | Light, EM waves, waves on a string | Sound waves, P-waves |
| Visualisation | Rope shaken up and down | Slinky pushed and pulled |
| Travels through vacuum? | EM waves: yes | No (needs a medium) |
Direction of particle oscillation
Transverse
Longitudinal
Can be polarised?
Transverse
Longitudinal
Examples
Transverse
Longitudinal
Visualisation
Transverse
Longitudinal
Travels through vacuum?
Transverse
Longitudinal
Full topic notes
Formal explanation with the rigour you need for the exam.
What are Waves?
At its core, a wave is a disturbance that transfers energy through a medium or space. Critically, while the energy travels, the particles of the medium itself only oscillate about their equilibrium positions; they do not get carried along with the wave. This distinction is vital for understanding how waves work.
Transverse Waves
In a transverse wave, the oscillations of the particles in the medium are perpendicular to the direction in which the wave's energy is travelling. Imagine shaking one end of a rope up and down; the wave moves horizontally along the rope, but each part of the rope only moves vertically.
7.2 Transverse and longitudinal waves.
Transverse waves are waves where the particles vibrate perpendicular along the lines of motions and consists of a series of “ crest ” and “ troughs ”.
Examples include electromagnetic waves, water ripples and vibration on a guitar string.
Longitudinal waves are waves where the particles vibrate along the lines of motion and consist of a series of compression and expansions (rarefractions).
Examples include sound waves.
Visual and graphical representation of transverse waves.
Longitudinal Waves
Conversely, in a longitudinal wave, the particles of the medium oscillate parallel to the direction of energy transfer. Picture pushing and pulling on a Slinky spring; the disturbance moves along the spring, and each coil moves back and forth in the same direction.
Particles oscillate parallel to energy propagation.
Consist of alternating regions: compressions (high pressure/density) and rarefactions (low pressure/density).
Sound waves are the most common example of longitudinal waves.
Longitudinal waves require a physical medium (solid, liquid, or gas) to travel and cannot pass through a vacuum.
Key Wave Properties
To describe waves quantitatively, we use several fundamental properties. Wavelength (λ) is the distance between two identical points on consecutive waves. Frequency (f) is how many full waves pass a point per second, while Period (T) is the time for one complete wave to pass.
The relationship between period and frequency is: .
The universal wave equation links speed, frequency, and wavelength: .
A displacement-distance graph helps visualise wavelength (λ).
A displacement-time graph helps visualise the period (T).
Frequency is measured in Hertz (Hz), where 1 Hz = 1 s⁻¹.
Wavelength is measured in metres (m).
The Phenomenon of Polarisation
Polarisation is a special characteristic where the oscillations of a transverse wave are restricted to a single plane. Imagine light waves oscillating in all directions perpendicular to their travel path. A polarising filter acts like a vertical fence, only allowing oscillations in the vertical plane to pass through.
For polarised light, Malus' Law describes the intensity after passing through a second filter, where is the initial intensity and is the angle between the wave's plane of oscillation and the polariser's axis.
Only transverse waves can be polarised; this provides definitive evidence of their transverse nature.
Longitudinal waves cannot be polarised as their oscillations are already restricted to the direction of travel.
Passing unpolarised transverse waves through a polarising filter reduces their intensity.
The intensity (I) of any wave is proportional to the square of its amplitude (A): I \propto A^2.
Always remember the core distinction: Transverse waves 'wiggle' perpendicular to energy flow, while longitudinal waves 'push-pull' parallel. This fundamental difference is key to understanding polarisation and predicting wave behaviour in exams.
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A wave on a string has frequency and wavelength . Calculate wave speed and state whether the wave is transverse on a shaken string.
- 1
.
Compare transverse and longitudinal waves: state one example of each and whether it can be polarised.
- 1
Transverse: light — oscillations perpendicular to travel; can be polarised.
How it all connects
The big idea sits in the middle — tap a linked idea to explore the link.
Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.
Glossary
Key terms for this topic — skim now; the Check step will test them.
- transverse wave
In a transverse wave, the oscillations of the particles in the medium are perpendicular to the direction in which the wave's energy is travelling.
- longitudinal wave
Conversely, in a longitudinal wave, the particles of the medium oscillate parallel to the direction of energy transfer.
- Wavelength
To describe waves quantitatively, we use several fundamental properties. Wavelength (λ) is the distance between two identical points on consecutive waves. Frequency (f) is how many full waves pass a point per second, while Period (T) is the time for one complete wave to pass.
- Polarisation
Polarisation is a special characteristic where the oscillations of a transverse wave are restricted to a single plane.
Sort it out
One statement at a time, say which heading it belongs under. Every statement comes from this lesson’s side-by-side comparison.
Slinky pushed and pulled
Quick check
Write your answer first, then compare it with the model one — the gap is what you would have lost.
Teach it back
If you can explain it simply, you own it — gaps here are marks you’d lose.
Teach it back
Explain this topic as if teaching a friend. We name the gaps an examiner would still dock.
Revision flashcards
Guess first, then flip — retrieval beats re-reading.
Key takeaways
Review these before you close the topic — retrieval beats re-reading.
7.2 Transverse and longitudinal waves.
Transverse waves are waves where the particles vibrate perpendicular along the lines of motions and consists of a series of “ crest ” and “ troughs ”.
Examples include electromagnetic waves, water ripples and vibration on a guitar string.
Longitudinal waves are waves where the particles vibrate along the lines of motion and consist of a series of compression and expansions (rarefractions).
Examples include sound waves.
Visual and graphical representation of transverse waves.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
With reference to the direction of transfer of energy, compare the oscillations of transverse and longitudinal progressive waves.
Extra simulations & links
PhET, GeoGebra and other curated tools — open in a new tab.
Frequently asked
Checkpoint
One marked question is worth ten re-reads — close the loop before you move on.
Reading it isn’t knowing it — prove it.
Before you move on: do 9702/22 · Q4(a) on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.
Discuss Transverse and longitudinal waves
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