Transverse and longitudinal waves — AQA GCSE Physics

SPEC 4.6.1.1 • WAVES — TRANSVERSE & LONGITUDINAL

Transverse & Longitudinal Waves

Module 6 opens with vocabulary. Get wavelength, amplitude, frequency and period locked in here — every wave topic that follows depends on it.

What Is A Wave?

Before you can describe waves with numbers, you need to know what a wave actually does — and what it doesn't do.

Wave [DEF]

A disturbance that transfers energy without transferring matter.

The Big Idea

Particles in the medium oscillate about their rest position — they do not travel with the wave. The wave moves; the matter stays roughly where it started.

Think of a Mexican wave in a stadium: the wave travels around the stadium, but each person stays in their seat. Energy passes along; the people don't.

Evidence — Wave Travels, Not The Medium

The spec asks you to describe evidence that it's the wave, not the water or air, that travels. Two concrete examples — one for each medium in the spec.

Ripples On Water

Float a cork, leaf, or rubber duck on the surface of a pond. Generate ripples by dropping a stone.

Observation: the float bobs up and down in roughly the same spot — it doesn't travel with the ripples to the edge of the pond. The water itself isn't moving outward; only the disturbance is.

Sound Waves In Air

A vibrating drum skin produces a loud sound that reaches your ears across the room.

Observation: the air does not get blown away from the drum — no vacuum forms next to it. You don't feel wind on your face when someone speaks across the room. The energy reaches your ear; the air doesn't.

Exam Phrasing That Scores

A 1-mark answer needs one clear piece of evidence — not just "the wave transfers energy". State the observation: "a floating object bobs up and down without travelling along with the wave" or "the drum does not create a vacuum / does not blow the air away". The observation IS the evidence.

Transverse Waves

The first of the two wave types. Definition first — then the picture that makes it stick.

Transverse Wave [DEF]

A wave in which the oscillations are perpendicular to the direction of energy transfer.

Key feature: oscillation goes across (perpendicular) the direction of travel. Drawn as a sine curve with crests (peaks) and troughs (valleys).

Transverse — Examples

Learn these by heart. AQA explicitly examines whether you can identify which type a given wave is.

Examples of Transverse Waves

All electromagnetic waves — light, radio, microwaves, infrared, UV, X-rays, gamma rays

Ripples on water (effectively transverse near the surface)

Waves on a stretched string (e.g. a vibrating guitar string)

Secondary (S) seismic waves from earthquakes

Memory Hook

"Light is transverse — sound is longitudinal." If you only remember one pair, remember this one. Light and all EM waves are transverse. Always.

Longitudinal Waves

The other type. Same idea — disturbance carrying energy — but the oscillation lines up with the direction of travel, not across it.

Longitudinal Wave [DEF]

A wave in which the oscillations are parallel to the direction of energy transfer.

Key feature: instead of crests and troughs, longitudinal waves have compressions (high-pressure regions where particles are bunched up) and rarefactions (low-pressure regions where particles are spread out).

Longitudinal — Examples

Shorter list than transverse — but high-frequency on exam papers.

Examples of Longitudinal Waves

Sound waves in air (and in any fluid)

Primary (P) seismic waves from earthquakes

Compression waves along a slinky spring pushed at one end

P and S Waves Preview

Earthquakes produce both: P-waves are longitudinal, S-waves are transverse. P-waves travel through solids and liquids; S-waves only through solids. That's how we know the Earth's outer core is liquid — but more on that in Lesson 6.04.

Side By Side

The cleanest way to lock the difference in: compare them directly.

PropertyTransverseLongitudinal

Oscillation directionPerpendicular to energy transferParallel to energy transfer

FeaturesCrests and troughsCompressions and rarefactions

ExamplesLight, all EM, water ripples, S-wavesSound, P-waves

Common shapeSine curvePressure variation (bunched lines)

What's The Same?

Both transfer energy without transferring matter. Both can be described by wavelength, amplitude, frequency, and period. The four properties on the next slides apply to both types.

Wavelength (λ)

First of the four wave properties. The Greek letter lambda (λ) is its symbol.

Wavelength λ [DEF]

The distance from a point on one wave to the equivalent point on the adjacent wave (e.g. crest to crest, or trough to trough). Measured in metres (m).

Don't Confuse

Wavelength is a horizontal measurement (along the direction of travel). It is not the height of the wave — that's amplitude, coming next.

Amplitude

How "big" the wave is. The mistake is measuring from crest to trough — that's twice the amplitude.

Amplitude [DEF]

The maximum displacement of a point on a wave from its undisturbed (rest) position. Measured in metres (m).

Amplitude tells you about energy. A wave with a bigger amplitude carries more energy. For sound, bigger amplitude = louder. For light, bigger amplitude = brighter.

Frequency (f)

Not "how many waves" — but how many per second. The "per second" part is where students lose marks.

Frequency f [DEF]

The number of complete waves passing a point per second. Measured in hertz (Hz).

Low Frequency

Few waves pass per second. Long wavelength. Example: a deep bass note, or a radio wave.

High Frequency

Many waves pass per second. Short wavelength. Example: a high-pitched whistle, or a gamma ray.

Unit Watch

1 Hz = 1 wave per second.kHz = thousands of waves/second. MHz = millions/second. GHz = billions/second. Convert all to Hz before using any equation (Lesson 6.02 will use this constantly).

Period (T)

The flip-side of frequency. If frequency asks "how many per second?", period asks "how many seconds per one?"

Period T [DEF]

The time taken for one complete wave to pass a point. Measured in seconds (s).

The Link (preview of Lesson 6.02)

Period and frequency are reciprocals:

T = 1 / f

A 50 Hz wave has a period of 1/50 = 0.02 s. A 200 Hz wave has period 0.005 s. Higher frequency → shorter period. This equation is on the AQA equation sheet — you don't need to memorise it.

All Four On One Diagram

Combine everything on a single labelled wave. This is the single most-asked diagram type in Module 6.

Applies To Both Wave Types

This sine curve shows a transverse wave, but all four properties — λ, amplitude, f, T — apply to longitudinal waves too. For longitudinal waves, λ is the distance between adjacent compressions (or adjacent rarefactions), and amplitude relates to the maximum density change.

Recall Check

If you can label λ, amplitude, and T on a blank wave diagram without looking, you've got the foundation. If not, redraw it now from memory before moving on.

Examiner Alert

This is the single biggest error AQA flagged on this topic — straight from the Jun 2024 examiner report.

Jun 2024 Paper 2 Q6.1

The examiner report noted that some students wrote that electromagnetic waves are "both transverse and longitudinal", and others focused on the uses of EM waves rather than the wave property the question was asking about.

The rules — no exceptions:

All electromagnetic waves are transverse — never longitudinal.

Sound waves are longitudinal — never transverse.

P-waves: longitudinal. S-waves: transverse.

Read The Command Word

If the question says "describe a property of EM waves", the answer is about the wave behaviour (transverse, travels at 3 × 10⁸ m/s, transfers energy). It is not a list of uses. Match your answer to the command word.

Weak vs Strong

Same question. Two answers. The difference is the language that AQA mark schemes actually credit.

"What does it mean to say that a wave transfers energy?"

✗ Weak

"Waves transfer matter from one place to another."

Wrong. Confuses energy transfer with mass transfer — a fundamental error on this topic. Scores 0 marks.

✓ Strong

"Waves transfer energy without transferring matter. Particles oscillate about their rest position but do not travel with the wave."

Names the key idea (energy, not matter) and the mechanism (particles oscillate, don't translate). Scores 2 marks.

Phrase To Memorise

"Energy without matter" + "particles oscillate about rest position" — those two phrases score on every "what is a wave" question.

Common Errors

Each of these is documented in AQA examiner reports. Learn the right version of each.

Students often writeCorrect version

"EM waves are longitudinal" or "both"All EM waves are transverse — never longitudinal

"Waves transfer matter"Waves transfer energy ; matter oscillates but doesn't travel with the wave

Wavelength = the height of the waveAmplitude is the height (rest → max). Wavelength is the horizontal distance between identical points

Amplitude = crest-to-trough distanceAmplitude is rest position → max displacement only . Crest-to-trough = 2 × amplitude

Frequency in kHz substituted into v = fλConvert to Hz first (×1000) before substituting

Practice Question

A guitar string vibrates and produces a sound wave that travels through the air to a listener.

(a) State the type of each wave: the wave on the string and the sound wave in the air. 2 marks

(b) Explain how a wave can carry sound from the guitar to the listener even though no matter travels between them. 3 marks

(a)

1

Wave on the string: transverse — the string oscillates perpendicular to the direction the wave travels along it. (1 mark)

2

Sound wave in the air: longitudinal — air particles oscillate parallel to the direction the wave travels. (1 mark)

(b) — PEE structure

P

A wave transfers energy without transferring matter. (1 mark)

E

In a sound wave, air particles oscillate back and forth about their rest position, creating compressions and rarefactions. (1 mark)

E

The compressions and rarefactions pass the energy from particle to particle through the air, so the energy reaches the listener even though the air molecules themselves stay roughly where they started. (1 mark)

PEE Walk-Through

Worked example for an extended explain question. Notice how each PEE step adds a layer the mark scheme can credit.

"Explain the key difference between a transverse and a longitudinal wave. (3 marks)"

P

Point. The difference is in the direction the particles oscillate relative to the direction the wave travels.

E

Evidence. In a transverse wave, particles oscillate perpendicular to the direction of energy transfer — for example, ripples on water, or light. In a longitudinal wave, particles oscillate parallel to the direction of energy transfer — for example, sound in air.

E

Explain. Because of this difference, transverse waves form crests and troughs whereas longitudinal waves form compressions and rarefactions — these are the two different ways the medium can be disturbed while still carrying energy.

Why It Scores

The Point names the underlying variable. The Evidence cites named examples for both types. The Explain links the cause (oscillation direction) to the consequence (crests/troughs vs compressions/rarefactions). That's the structure AQA examiners credit.

Lesson Summary

You should now be confident on every item below. If any are shaky, revisit the relevant slide before moving on to Lesson 6.02.

✓ Checkpoint — You Can Now…

State that a wave transfers energy without transferring matter

Describe evidence that the wave (not the medium) travels — floating object bobbing on water, drum not creating a vacuum

Define transverse (oscillation perpendicular) and give examples — light, all EM, water ripples

Define longitudinal (oscillation parallel) and give examples — sound, P-waves

Define and label wavelength (λ, in m), amplitude (m), frequency (f, in Hz), period (T, in s)

State the rule: EM = always transverse; sound = always longitudinal

Write a 3-mark PEE answer comparing the two wave types

Coming Next — Lesson 6.02

Properties of waves & RP8. The two equations linking everything in this lesson: v = f λ (wave speed equation) and T = 1 / f. Plus the ripple-tank + stretched-string practical — one of the most reliably examined RPs in Paper 2.