What are the main differences between transverse and longitudinal waves?

Transverse waves are characterized by particle displacement perpendicular to the direction of wave propagation, such as light waves. Longitudinal waves, like sound waves, involve particle displacement parallel to the direction of wave propagation. Understanding these differences is crucial for Cambridge International A Levels Physics as it helps in analyzing wave behaviors in various media.

How do transverse and longitudinal waves propagate through different media?

Transverse waves typically require a medium that can support shear stress, such as solids, while longitudinal waves can propagate through solids, liquids, and gases. This is because longitudinal waves rely on compressions and rarefactions, which can occur in any medium. This concept is important in the Cambridge International A Levels curriculum to understand wave mechanics.

Can you provide examples of transverse and longitudinal waves in everyday life?

Common examples of transverse waves include electromagnetic waves like light and radio waves, while sound waves in air are a classic example of longitudinal waves. Recognizing these examples helps students relate theoretical concepts from the Cambridge International A Levels Physics syllabus to real-world phenomena.

Why are transverse waves unable to travel through fluids?

Transverse waves require a medium that can resist changes in shape, which fluids cannot provide due to their inability to support shear stress. This limitation is a key point in the Cambridge International A Levels Physics curriculum, as it explains why only longitudinal waves can travel through fluids like water and air.

How do the speed and wavelength of transverse and longitudinal waves compare?

The speed of a wave depends on the medium and type of wave. Generally, transverse waves travel faster in solids, while longitudinal waves can vary in speed depending on the medium's density and elasticity. Wavelengths also differ based on frequency and speed. Understanding these relationships is essential for Cambridge International A Levels students studying wave dynamics.

Why is "Saying sound is transverse" a common mistake in Transverse and longitudinal waves?

Why it happens: Sound waves drawn as sine curves. How to avoid it: Sound is LONGITUDINAL. The sine curve represents pressure vs position, not particle displacement perpendicular to motion. Source: 9702 Examiner Reports 2022-2024

Why is "Saying EM waves need a medium" a common mistake in Transverse and longitudinal waves?

Why it happens: Sound needs air. How to avoid it: EM waves (transverse) propagate through vacuum. Sound (longitudinal) requires medium. Source: 9702 Examiner Reports 2022-2024

WavesCambridge International A Level Physics 9702

Transverse and longitudinal waves

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Short Study Notes — Transverse and longitudinal waves

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Transverse and Longitudinal Waves Study Notes — Cambridge International A Level Physics 9702 (2025-2027 syllabus)

Two fundamental wave classes. Light vs sound. Polarisation possibility.

What you’ll learn

Mapped to the Cambridge International A Level 9702 syllabus (2025-2027).

7.2.1 — Distinguish transverse and longitudinal waves.
7.2.2 — Identify examples.
7.2.3 — Describe compression and rarefaction.

Wave types

Perpendicular or parallel oscillation.

Transverse. Particle oscillation PERPENDICULAR to direction of wave travel.

Examples: light (and all EM), water surface waves, seismic S-waves, string on guitar.
CAN be polarised.

Longitudinal. Particle oscillation PARALLEL to direction of wave travel.

Examples: sound in air, P-waves, ultrasound.
CANNOT be polarised.

Compressions and rarefactions are the longitudinal wave's equivalent of crests and troughs.

Compression: particles bunched; high pressure/density.
Rarefaction: particles spread; low pressure/density.

Cambridge tip. Memorise typical examples of each.

In a transverse wave particles oscillate perpendicular to the travel direction; in a longitudinal wave they oscillate parallel, forming compressions and rarefactions.

Transverse: perpendicular oscillation.
Longitudinal: parallel oscillation.
Only transverse can polarise.

See the full worked example for transverse and longitudinal waves →

Sound and EM waves

Two key examples.

Sound. Longitudinal pressure waves in matter. Requires a medium.

Speed in air at room temperature: $\approx 343$ m/s. Increases with temperature; faster in solids and liquids than in gases.

Electromagnetic waves. Transverse. Electric and magnetic field oscillations perpendicular to each other AND to direction of travel.

Speed in vacuum: $c = 3.00 \times 10^8$ m/s. Does NOT need a medium.

Cambridge tip. EM waves don't need a medium — KEY distinction.

Sound: longitudinal, needs medium.
EM: transverse, travels in vacuum.
Speeds: sound ~340 m/s; light $3 \times 10^8$ m/s.

See the full worked example for transverse and longitudinal waves →

Compression and rarefaction

Longitudinal wave features.

Compression. Region where particles are BUNCHED together. High pressure and density.

Rarefaction. Region where particles are SPREAD apart. Low pressure and density.

Wavelength. Distance between adjacent compressions (or adjacent rarefactions).

Visualisation. Sound is often drawn as a sine wave plotting pressure vs position — but particle motion is along wave direction, not perpendicular.

Cambridge tip. When asked to sketch longitudinal wave, label particles and motion direction.

Compression: bunched/high pressure.
Rarefaction: spread/low pressure.
Particles oscillate parallel to motion.

See the full worked example for transverse and longitudinal waves →

How it’s examined

Wave types in every Paper 1. Most-tested: classification (5 marks), sketch & label (4-5 marks).

Sources: Cambridge International A Level Physics 9702 syllabus (2025-2027); 9702 Examiner Reports 2022-2024; 9702/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-11.

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Step-by-step worked examples — Transverse and longitudinal waves

Step-by-step solutions to past-paper-style questions on transverse and longitudinal waves, written exactly the way a tutor would explain them at the board.

1Wave type identification (5 marks)
Extended• Adapted from 9702/22 May/Jun 2024• wave types
Question
Classify each as transverse or longitudinal: (a) sound in air, (b) light, (c) ripples on water, (d) seismic P-waves, (e) seismic S-waves. (5 marks)
Step-by-step solution
1. Step 1
  (a) Sound in air: LONGITUDINAL. Particles oscillate parallel to wave direction.
2. Step 2
  (b) Light: TRANSVERSE. Electric and magnetic fields oscillate perpendicular.
3. Step 3
  (c) Water ripples: TRANSVERSE (approximately).
4. Step 4
  (d) P-waves: LONGITUDINAL. Primary, faster, travel through solid AND liquid.
5. Step 5
  (e) S-waves: TRANSVERSE. Secondary, slower, only through solids.
Answer
(a) Long, (b) Trans, (c) Trans, (d) Long, (e) Trans.
2Speed of sound (5 marks)
Extended• sound
Question
A 256 Hz tuning fork produces sound with wavelength 1.32 m. Find the speed of sound. (5 marks)
Step-by-step solution
1. Step 1
  $v = f\lambda$ .
  $v = 256 \times 1.32 \approx 338 \text{ m/s}$
Answer
$v \approx 338$ m/s.
3Compression/rarefaction (4 marks)
Extended• longitudinal
Question
Sketch a longitudinal wave. Label compressions and rarefactions. Describe particle motion. (4 marks)
Step-by-step solution
1. Step 1
  Compression. Particles bunched together; high pressure.
2. Step 2
  Rarefaction. Particles spread apart; low pressure.
3. Step 3
  Particles oscillate parallel to wave direction. No net displacement.
Answer
Compression = bunched; rarefaction = spread. Parallel motion.

Key Definitions and Keywords — Transverse and longitudinal waves

Definitions to memorise and the exact keywords mark schemes credit for transverse and longitudinal waves answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9702 sitting.

Transverse wave
Examiner keyword
Particle oscillation PERPENDICULAR to direction of energy travel. Can be polarised. Examples: light, water ripples, S-waves.
Longitudinal wave
Examiner keyword
Particle oscillation PARALLEL to direction of energy travel. Cannot be polarised. Compressions and rarefactions. Examples: sound, P-waves.
Compression
Examiner keyword
Region of high particle density and pressure in longitudinal wave.
Rarefaction
Examiner keyword
Region of low particle density and pressure.

Common Mistakes and Misconceptions — Transverse and longitudinal waves

The traps other students keep falling into on transverse and longitudinal waves questions — taken from recent Cambridge International A Level 9702 examiner reports and mark schemes — and how to avoid them.

✕Saying sound is transverse
9702 Examiner Reports 2022-2024
Why it happens
Sound waves drawn as sine curves.
How to avoid it
Sound is LONGITUDINAL. The sine curve represents pressure vs position, not particle displacement perpendicular to motion.
✕Saying EM waves need a medium
9702 Examiner Reports 2022-2024
Why it happens
Sound needs air.
How to avoid it
EM waves (transverse) propagate through vacuum. Sound (longitudinal) requires medium.

Practice questions

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Transverse and longitudinal waves — frequently asked questions

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Transverse and longitudinal waves

Short Study Notes in the form of Slides

Short Study Notes — Transverse and longitudinal waves

Detailed Notes

What you’ll learn

How it’s examined

1Wave type identification (5 marks)

2Speed of sound (5 marks)

3Compression/rarefaction (4 marks)

Transverse wave

Longitudinal wave

Compression

Rarefaction

✕Saying sound is transverse

✕Saying EM waves need a medium

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Transverse and longitudinal waves — frequently asked questions