Transverse and longitudinal waves — AQA GCSE Combined Science
Test yourself on Transverse and longitudinal waves with AQA GCSE practice questions.
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Transverse and longitudinal waves explained
Waves are classified by how the oscillations relate to the direction of energy transfer.
Read the full explanation
In a transverse wave, the oscillations are perpendicular to the direction of energy transfer; examples include light, water surface waves and waves on a rope. In a longitudinal wave, the oscillations are parallel to the direction of energy transfer; examples include sound and ultrasound. Longitudinal waves show compressions, where particles are closer together, and rarefactions, where particles are further apart. You can identify the type from a diagram by checking whether the disturbance is at right angles to the wave direction or along it. This classification helps explain wave behaviour such as polarisation, which only transverse waves can show.
The ripples on a water surface are an example of a transverse wave.
A transverse wave transfers energy without transferring matter, and its oscillations are perpendicular to the direction of energy travel. Water-surface ripples demonstrate this: a floating cork bobs up and down while the ripple pattern moves horizontally across the surface, so the particles oscillate vertically while the wave travels horizontally. The wave carries energy from a disturbance, such as a dropped stone, outwards, but the water itself does not travel with the wave. You can identify transverse waves by their perpendicular oscillation and by features such as crests and troughs. Other examples include waves on a rope shaken up and down and all electromagnetic waves. In an exam, describe the direction of vibration relative to energy transfer and use the cork or crest-and-trough pattern as evidence.
Longitudinal waves show areas of compression and rarefaction. Sound waves travelling through air are longitudinal.
In a longitudinal wave, the oscillations are parallel to the direction of energy transfer. Sound travelling through air is longitudinal: air particles vibrate back and forth along the same line as the sound travels, creating regions where particles are crowded together (compressions) and regions where they are spread apart (rarefactions). These pressure variations pass through the air and are detected as sound. A compression is a region of higher pressure and density; a rarefaction is a region of lower pressure and density. The pattern moves forward, but the air particles themselves oscillate about fixed positions and do not travel with the sound. You can represent this with a slinky spring pushed and pulled along its length, or by a series of alternating dense and sparse dots.
Students should be able to describe the difference between longitudinal and transverse waves.
Waves transfer energy from one place to another without transferring matter. The key difference is the direction in which the particles of the medium vibrate compared with the direction in which the wave travels. In a transverse wave, the vibrations are at right angles (perpendicular) to the direction of energy transfer; examples include light, water surface ripples and waves on a rope shaken up and down. In a longitudinal wave, the vibrations are along the same line as the direction of energy transfer, producing regions of compression and rarefaction; sound in air is the standard example. A useful check is to trace the wave direction and then ask whether the oscillation is across it or back and forth along it. Transverse waves can be polarised, whereas longitudinal waves cannot, which is a further distinguishing feature.
Students should be able to describe evidence that, for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels.
A wave transfers energy through a medium while the medium itself stays in place. For water ripples, a small floating object such as a cork or leaf bobs up and down as a ripple passes but does not move along with the ripple; this shows the water oscillates about a fixed position while the wave pattern travels outward. For sound in air, a smoke trail or a lightweight suspended object in a tube shows local vibration of air but no steady flow of air from the source to the listener; the sound is heard because compressions and rarefactions travel through the air. In both cases the wave, meaning the disturbance and its energy, moves from source to detector, while the particles of water or air only vibrate about equilibrium positions. This distinguishes wave travel from bulk movement of matter.
Your focus
- Define transverse and longitudinal waves in terms of the direction of oscillation relative to the direction of energy transfer.
- Give examples of transverse and longitudinal waves.
- Identify compressions and rarefactions in a longitudinal wave.
Show all 15 objectives
- Identify water-surface ripples as a transverse wave.
- Describe the perpendicular relationship between oscillation and energy transfer in a transverse wave.
- Explain how a floating object demonstrates that water particles oscillate rather than travel with the wave.
- Define compression and rarefaction in terms of particle spacing and pressure.
- Describe sound travelling through air as a longitudinal wave.
- Explain how compressions and rarefactions transfer energy through air without transferring air particles over long distances.
- Define transverse and longitudinal waves in terms of the direction of vibration relative to energy transfer.
- Classify given examples, such as light, water ripples and sound, as transverse or longitudinal.
- Explain how compressions and rarefactions arise in a longitudinal wave.
- Describe observations that show a medium does not travel with a wave.
- Explain how floating markers and sound demonstrations provide evidence for wave travel.
- Distinguish between the movement of a wave and the vibration of particles in the medium.
Transverse and longitudinal waves exam tips
Marking Points
- State that in a transverse wave the oscillations are perpendicular to the direction of energy transfer.
- State that in a longitudinal wave the oscillations are parallel to the direction of energy transfer.
- Give a correct example of a transverse wave, such as light, water surface waves or a wave on a rope.
- Give a correct example of a longitudinal wave, such as sound or ultrasound.
- Identify compressions and rarefactions in a longitudinal wave diagram or description.
- Use a diagram to classify a wave as transverse or longitudinal by comparing the oscillation direction with the direction of energy transfer.
- State that a transverse wave has oscillations perpendicular to the direction of energy transfer.
- Describe water ripples as a transverse wave in which surface particles move up and down while the wave travels horizontally.
- Explain that the wave transfers energy across the surface without transferring water from one place to another.
- Use a floating object, such as a cork, bobbing vertically as evidence that the oscillation is perpendicular to the wave direction.
- Identify crests and troughs as the high and low points of a transverse water wave.
- Compare water ripples with another transverse example, such as a wave on a rope or an electromagnetic wave.
- State that longitudinal waves have oscillations parallel to the direction of energy transfer.
- Define compression as a region where particles are closer together, with higher pressure or density.
- Define rarefaction as a region where particles are further apart, with lower pressure or density.
- Describe sound travelling through air as a longitudinal wave in which air particles vibrate back and forth along the direction of travel.
- Explain that the compressions and rarefactions travel through the air while the air particles oscillate about fixed positions.
- Use a slinky spring or a particle diagram to model alternating compressions and rarefactions.
- States that in a transverse wave the oscillations or vibrations are perpendicular (at right angles) to the direction of energy transfer or wave travel.
- States that in a longitudinal wave the oscillations or vibrations are parallel to the direction of energy transfer or wave travel.
- Identifies compressions and rarefactions as the regions of high and low pressure or density in a longitudinal wave.
- Gives a correct example for each type, such as light or water ripples for transverse and sound in air for longitudinal.
- Recognises that both wave types transfer energy without transferring matter overall.
- Notes that transverse waves can be polarised while longitudinal waves cannot.
- Describes a floating marker on water that moves up and down but does not travel along with the ripple.
- Explains that the water particles oscillate about fixed positions while the ripple pattern moves outward.
- Describes a demonstration with sound, such as a smoke trail or suspended light object, showing air vibrating without a steady flow from source to detector.
- States that in both cases it is the wave or disturbance that travels and transfers energy, not the medium as a whole.
- Links the observation to the idea that particles vibrate about equilibrium positions rather than being carried along.
- Uses the terms transverse and longitudinal correctly when describing the two examples.
Examiner Tips
- 💡Use the words perpendicular and parallel accurately when defining transverse and longitudinal waves.
- 💡When labelling a longitudinal wave, mark a compression and a rarefaction clearly and state what each means.
- 💡If a diagram is given, state the direction of energy transfer and the direction of oscillation before naming the wave type.
- 💡Define transverse by the perpendicular relationship between oscillation and energy transfer before giving the water-ripple example.
- 💡Use a labelled diagram or a described cork to show the vertical oscillation and horizontal wave travel.
- 💡Link the example to energy transfer without matter transfer, since this is the key property of all waves.
- 💡Define compression and rarefaction in terms of particle spacing and pressure before applying them to sound.
- 💡Use a slinky spring or a dot diagram to show how compressions and rarefactions move along the direction of travel.
- 💡State clearly that sound in air is longitudinal, and avoid using crest and trough language for it.
- 💡Define the reference direction first: state the direction of energy transfer, then describe the vibration direction relative to it.
- 💡Use the words perpendicular and parallel explicitly, since vague phrases such as 'side to side' may not gain credit.
- 💡Support each definition with one named example to show understanding rather than repeating the definition.
- 💡If a diagram is given, annotate the vibration direction and the wave travel direction with arrows before writing your answer.
- 💡Name the observation and then state what it proves, for example 'the cork stays in place, so the water does not travel with the wave'.
- 💡Use the phrase 'vibrate about fixed positions' to make the distinction between particle motion and wave travel clear.
- 💡For sound, refer to compressions and rarefactions moving through the air rather than air moving as a whole.
- 💡Keep the two examples separate in your answer so each piece of evidence is clearly linked to its wave type.
Common Mistakes
- Saying that in a transverse wave the wave moves up and down. Correction: describe the oscillation as perpendicular to the direction of energy transfer, not simply up and down.
- Confusing compressions with rarefactions. Correction: compressions are regions where particles are closer together; rarefactions are regions where particles are further apart.
- Thinking sound is transverse because it can be drawn as a wave. Correction: sound is longitudinal; the oscillations of particles are parallel to the direction of energy transfer.
- Saying the water travels along with the wave; correct this by stating that energy is transferred while the water particles oscillate about fixed positions.
- Describing the oscillation as parallel to the wave direction; correct this by stating that transverse oscillations are perpendicular to energy transfer.
- Confusing crests with compressions; correct this by reserving crest and trough for transverse waves and compression and rarefaction for longitudinal waves.
- Labelling compressions and rarefactions as crests and troughs; correct this by using compression and rarefaction for longitudinal waves.
- Claiming that air particles travel from the source to the listener; correct this by stating that energy is transferred through particle oscillations while the particles remain near fixed positions.
- Describing sound as transverse because it can be drawn as a wave; correct this by stating that sound in air is longitudinal, with oscillations parallel to energy transfer.
- Confusing the two types by saying transverse waves vibrate along the direction of travel; correct this by linking transverse to perpendicular and longitudinal to parallel.
- Thinking that the medium itself travels with the wave; correct this by stressing that particles oscillate about fixed positions while energy is transferred.
- Describing compressions as places where particles are stationary; correct this by explaining that particles in a compression are closer together and still vibrating.
- Assuming all waves are transverse; correct this by recalling that sound and some seismic waves are longitudinal.
- Claiming that water moves outward with the ripple; correct this by citing the floating object that only bobs up and down.
- Saying that air travels from the source to the ear; correct this by explaining that compressions and rarefactions pass through the air while air particles vibrate locally.
- Treating the wave as a physical object that is carried along; correct this by defining a wave as a disturbance that transfers energy through a medium.
- Ignoring the medium entirely and saying no particles are involved; correct this by stating that particles vibrate but do not travel with the wave.