SEC G3 Combined Science Physics component K326/K327
CP9: General Wave Properties, including sound
Use wave quantities, transverse and longitudinal models, sound, and echo reasoning.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
A wave is a travelling disturbance that transfers energy while the particles of a medium, when present, oscillate around their positions.
Wave motion and wave quantities
Ropes, springs, and ripple tanks show how a disturbance and its wavefront move. A wavefront joins points that are at the same phase of an oscillation. The medium does not travel with the wave overall, even though its particles oscillate as energy passes.
Amplitude is the greatest displacement from equilibrium, wavelength is the spacing between adjacent points in the same phase, frequency is cycles per second, and period is time per cycle. Wave speed equals frequency times wavelength.
Transverse, longitudinal, and sound waves
In a transverse wave, oscillation is perpendicular to travel, as for a wave on a rope, a ripple-tank surface wave, or an electromagnetic wave. In a longitudinal wave, oscillation is parallel to travel, producing compressions and rarefactions, as for sound in air or a compressed spring.
Sound begins with a vibrating source and needs a medium. Greater amplitude is heard as greater loudness, while greater frequency is heard as higher pitch.
Echoes and distance
An echo is reflected sound received after a delay. The measured time includes the outward and return journeys.
For a reflector distance, multiply sound speed by the total echo time and divide by two.
Formulae and relationships
| Relationship | Use |
|---|---|
| Relate wave speed, frequency, and wavelength. | |
| Relate period and frequency. |
Worked examples
Example 1: An echo returns after . Sound speed is . Find the reflector distance.
- Find the round-trip distance: .
- Recognise that the sound travels out and back.
- Divide by two to obtain .
Answer: .
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Relate amplitude, wavelength, frequency, period, and speed through a labelled representation.
- Distinguish transverse and longitudinal waves using vibration direction and explain sound through compressions and rarefactions.
- Use the sound wave's round trip when interpreting an echo or distance measurement.
Official outcome coverage
K326 CP9: 9 mapped outcomes, references CP9(a), CP9(b), CP9(c), CP9(d), CP9(e), CP9(f), CP9(g), CP9(h), CP9(i). Check the official K326 syllabus.
K327 CP9: 9 mapped outcomes, references CP9(a), CP9(b), CP9(c), CP9(d), CP9(e), CP9(f), CP9(g), CP9(h), CP9(i). Check the official K327 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Measure wave or echo behaviour using a known distance and a measured time or frequency. Record enough cycles to reduce timing percentage uncertainty, use the sound round trip where required, and separate the observed signal from the wave-model inference.
Exam traps and retrieval check
Avoid these traps
- Saying matter travels from source to receiver with the wave.
- Swapping amplitude with frequency when describing sound.
- Forgetting to halve an echo's round-trip distance.
Check from memory
What does a wave transfer?
Energy without net transfer of matter.
How do particles oscillate in a longitudinal wave?
Parallel to the direction of travel.
What determines pitch?
Frequency.
Official Combined Science scope
This shared Combined Physics owner serves both K326 and K327. Wave motion, energy transfer, wave quantities, transverse and longitudinal waves, sound, and echoes.