O-Level and SEC G3 Physics K323
P10: General Properties of Waves, including Sound
Connect wave quantities and representations, then apply reflection, refraction, diffraction, and sound reasoning.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Waves transfer energy without net transfer of matter. K323 connects wave quantities and representations to transverse and longitudinal motion, sound, echoes and ultrasound.
Wave quantities and motion
Amplitude is maximum displacement from equilibrium, wavelength is the distance between adjacent points in phase, frequency is cycles per second, and period is time per cycle. A wavefront joins points at the same phase.
Wave speed depends on frequency and wavelength. When a source changes frequency in the same medium, wavelength changes correspondingly. Medium particles oscillate around equilibrium rather than travelling with the wave over long distances.
Transverse, longitudinal and sound waves
In a transverse wave, vibration is perpendicular to energy-transfer direction. In a longitudinal wave, vibration is parallel, creating compressions and rarefactions. Sound in air is longitudinal and requires a material medium.
Greater sound-wave amplitude generally corresponds to greater loudness, while greater frequency corresponds to higher pitch. Do not confuse pitch with speed: in a given medium, different audible frequencies travel at approximately the same speed.
Echoes and ultrasound
An echo is reflected sound. For pulse-echo distance measurement, the measured time usually covers the outward and return paths, so the one-way distance is half of speed multiplied by time.
Ultrasound has frequency above human hearing. Sonar uses reflected pulses to measure underwater distance, while medical imaging uses partial reflections at tissue boundaries to construct information about internal structures.
Formulae and relationships
| Relationship | Use |
|---|---|
| Relate wave speed, frequency and wavelength. | |
| Relate period and frequency. | |
| Find one-way distance from a return echo. |
Worked examples
Example 1: A sonar pulse returns after . Sound speed in water is . Find the depth.
- The pulse travels down and back, so total path is twice the depth.
- Use .
- State the one-way depth, not the total pulse path.
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.
- Apply reflection, refraction, and diffraction to wavefronts and sound evidence.
Official outcome coverage
K323 P10: 10 mapped outcomes, references P10(a), P10(b), P10(c), P10(d), P10(e), P10(f), P10(g), P10(h), P10(i), P10(j). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Measure wave speed or sound behaviour from distance and time data, then connect uncertainty to the chosen timing or length method.
Exam traps and retrieval check
Avoid these traps
- Saying matter travels with the wave from source to receiver.
- Using crest-to-trough distance as one wavelength.
- Forgetting to halve a pulse-echo round-trip distance.
Check from memory
What is one wavelength in a longitudinal wave?
The distance between adjacent compressions or adjacent rarefactions.
Can sound travel in vacuum?
No, because it requires a material medium.
What determines pitch?
Frequency.
Pure versus Combined scope
Combined Physics revisits part of this core under CP9 General Wave Properties, including sound, but with reduced outcome scope. Combined students should follow the component checklist rather than assume every K323 outcome is assessable.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.