Transverse and Longitudinal Waves
PhysicsΒ· 30 min read
1. Transverse Wavesβ β ββββ± 12 min
Transverse Wave
A wave where particles of the medium oscillate perpendicular to the direction the wave travels (direction of energy propagation).
Example:
Waves on a stretched string, electromagnetic waves, surface water ripples
Transverse waves have distinct peaks (maximum positive displacement from equilibrium) and troughs (maximum negative displacement from equilibrium). A unique property of transverse waves is that they can be polarised, as the oscillation is restricted to one plane perpendicular to wave travel.
A transverse wave travels along a horizontal slinky from left to right. Describe the motion of a single coil in the slinky.
- 1
Recall the definition of a transverse wave: particle oscillation is perpendicular to wave direction of travel.
- 2
The wave travels horizontally, so oscillation must be vertical.
- 3
Waves transfer energy not matter, so the coil stays near its original equilibrium position.
- 4
Final answer: The coil oscillates up and down around its fixed starting position, it does not move left to right with the wave.
2. Longitudinal Wavesβ β β βββ± 15 min
Longitudinal Wave
A wave where particles of the medium oscillate parallel to the direction the wave travels (direction of energy propagation).
Example:
Sound waves in air, primary seismic waves, pressure waves in a slinky
Longitudinal waves do not have peaks and troughs. Instead, they have alternating regions of compression and rarefaction. Longitudinal waves cannot be polarised, because there is only one plane of oscillation parallel to the wave direction.
A sound wave travels horizontally from a speaker to your ear. Describe the motion of a single air particle along the wave path.
- 1
Sound waves are longitudinal, so particle oscillation is parallel to wave direction.
- 2
The wave travels horizontally, so the air particle oscillates horizontally back and forth.
- 3
Waves do not transfer matter, so the particle stays near its original equilibrium position.
- 4
Final answer: The particle oscillates horizontally back and forth around its fixed starting position, it does not travel from the speaker to your ear.
3. Comparisons and Exam Expectationsβ β β βββ± 10 min
Test your understanding:
Which of the following is a longitudinal wave?
A. Visible light
B. A vibrating guitar string wave
C. Speech sound from a mouth
D. Ripples on a lake
Reveal answer
C βCorrect! All sound waves in air are longitudinal. The other options are all transverse waves.
A compression in a longitudinal wave is:
A. Where particles are stationary
B. Where particles are closer than equilibrium
C. Where particles are further apart than equilibrium
D. Where the wave starts
Reveal answer
B βThat's right! Compressions are high pressure regions with particles closer together, rarefactions are low pressure regions with particles further apart.
4. Common Pitfalls
Wrong move:
Claiming that particles travel along with the wave from one end of the medium to the other.
Why:
Waves only transfer energy, not matter. All particles oscillate around a fixed equilibrium position.
Correct move:
State that particles oscillate around a fixed rest position and do not move with the wave.
Wrong move:
Claiming that all electromagnetic waves are longitudinal.
Why:
All electromagnetic waves are transverse by definition, regardless of frequency or wavelength.
Correct move:
Remember all EM waves are transverse, so they can be polarised.
Wrong move:
Confusing compressions and rarefactions as regions where particles do not move.
Why:
Particles oscillate through all regions of the wave; particles pass through equilibrium at the centre of a compression or rarefaction.
Correct move:
Label compressions as regions of maximum pressure (closest particles) and rarefactions as regions of minimum pressure (furthest particles).
Wrong move:
Claiming longitudinal waves cannot show interference or diffraction.
Why:
All wave types share all common wave properties except polarisation, which is exclusive to transverse waves.
Correct move:
Only polarisation is unique to transverse waves; interference, diffraction and reflection occur for both types.
5. Quick Reference Cheatsheet
Property | Transverse Wave | Longitudinal Wave |
|---|---|---|
Particle oscillation direction | Perpendicular to wave travel | Parallel to wave travel |
Key features | Peaks and troughs | Compressions and rarefactions |
Can be polarised? | Yes | No |
Common examples | EM waves, string waves, ripples | Sound, P-seismic waves |
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2023 Β· 1
Identify longitudinal wave example
- 2022 Β· 2
Compare wave types from diagram
- 2021 Β· 1
Describe particle motion in wave
Going deeper
What's Next
Classifying waves into transverse and longitudinal types is a fundamental concept that underpins all further wave topics in CIE A-Level Physics. This distinction explains why only transverse waves can be polarised, and helps you correctly interpret wave diagrams that appear regularly in both multiple choice and structured exam questions. Many exam questions will ask you to apply this definition to unfamiliar examples (such as seismic waves), so remember to rely on the core definition of particle oscillation direction, not just memorized examples. Next, you will explore key wave parameters, then move on to advanced wave phenomena like polarisation, interference and diffraction.