Who this is for: Cambridge IGCSE Physics (0625) students who want sound — longitudinal waves, pitch, loudness and ultrasound — to become reliable marks instead of facts they recall without linking frequency to what they hear.
What query it owns: how to understand and revise sound in Cambridge IGCSE Physics.
Why this is safe: this page owns the sound revision-guide angle, while Tutopiya’s Sound subtopic page owns the learning resource and the free Sound quiz owns the practice.

Sound is a core Cambridge IGCSE Physics (0625) topic tested through definitions, calculations and applications. Examiners expect you to describe sound as a longitudinal wave, explain pitch and loudness, state that sound needs a medium, and describe uses of ultrasound. This guide covers the syllabus content and the question types that appear every year.

Key takeaways

• Sound is a longitudinal wave — vibrations parallel to direction of travel; compressions and rarefactions.
• Sound cannot travel through a vacuum — it needs a medium (solid, liquid or gas).
• Pitch is determined by frequency (high frequency = high pitch); loudness by amplitude.
• Speed of sound in air ≈ 330–340 m/s (faster in solids than in gases).
• Ultrasound is sound above 20 000 Hz — used in scanning, cleaning and sonar.

What is sound in Cambridge IGCSE Physics?

Sound is a mechanical wave produced by vibrating sources. It transfers energy through a medium by causing particles to vibrate back and forth parallel to the direction of travel. In Cambridge IGCSE Physics (0625) you must describe how sound is produced and detected, interpret oscilloscope traces for pitch and loudness, and explain echo and ultrasound applications.

You can read the full explanation, worked examples and notes on Tutopiya’s Sound subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Longitudinal wave	Vibrations parallel to travel	”Describe how sound travels through air.”
Medium required	No sound in vacuum	”Explain why sound cannot travel in space.”
Pitch ↔ frequency	Higher f = higher pitch	”Which trace shows the higher pitch?”
Loudness ↔ amplitude	Larger amplitude = louder	”How does loudness change when amplitude doubles?”
Ultrasound	f > 20 kHz; medical and industrial uses	”State one use of ultrasound.”

Pitch vs loudness vs quality: what changes on the trace?

Property	Physical quantity	What you see on an oscilloscope
Pitch	Frequency	More waves per second → closer peaks
Loudness	Amplitude	Taller trace (greater displacement)
Quality (timbre)	Waveform shape	Different pattern for different instruments
Speed	Depends on medium	Does not change pitch or loudness

How to answer sound calculation questions — step by step

1. Identify what is given — distance, time, frequency or wavelength.
2. Choose the correct equation — v = fλ, or v = d/t for echo problems.
3. Convert units — kHz to Hz, km to m if needed.
4. Substitute and calculate with units in the answer.
5. For echoes, remember distance travelled = 2 × distance to reflector.

Once you have worked through a few, test yourself with the free Sound quiz.

Sound in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical sound stem
Define	Precise syllabus definition	”Define ultrasound.”
Describe	Features or mechanism	”Describe how sound is produced.”
Explain	Cause and effect	”Explain why sound travels faster in steel than in air.”
Calculate	Show formula and working	”Calculate the wavelength of a 170 Hz sound wave in air.”
State	Short factual answer	”State the approximate speed of sound in air.”

Worked exam-style stems (how to answer the wording)

1. “A sound wave in air has a frequency of 340 Hz. The speed of sound is 340 m/s. Calculate the wavelength.” λ = v/f = 340/340 = 1.0 m. Mark-scheme reward: rearrangement of v = fλ, correct answer with unit.
2. “Explain why astronauts on the Moon cannot hear each other without radios.” There is no atmosphere (vacuum) on the Moon → sound needs a medium to travel → cannot propagate between astronauts. Reward: no medium + sound is mechanical.
3. “State one use of ultrasound in medicine.” Scanning internal organs / prenatal scanning (or breaking kidney stones). Reward: valid medical application named.

When you can recognise the wording instantly, work the full set on the Waves topical past paper questions and the Sound quiz to lock the definitions in.

How sound connects to the rest of the syllabus

Sound builds on General Properties of Waves — especially v = fλ and longitudinal vs transverse. Ultrasound contrasts with audible sound in frequency only. The Cambridge IGCSE Physics resource hub links every Waves subtopic.

Common mistakes students make

• Describing sound as a transverse wave.
• Linking loudness to frequency (loudness depends on amplitude).
• Forgetting to double the distance in echo time-of-flight calculations.
• Stating sound can travel in a vacuum.
• Confusing ultrasound with infrasound (below 20 Hz).

When you need more support

If sound questions keep costing marks — especially oscilloscope traces and echo calculations — work through the Waves topical past paper questions and the Sound quiz, then get focused help from a Cambridge IGCSE Physics tutor.

Frequently asked questions

Is sound hard in Cambridge IGCSE Physics? The theory is accessible, but marks are lost when students confuse pitch with loudness or treat sound as transverse.

What is the range of human hearing? Approximately 20 Hz to 20 000 Hz. Below = infrasound; above = ultrasound.

Why is sound faster in solids than in gases? Particles are closer together in solids → energy is passed on more quickly between particles.

How do I revise sound effectively? Learn longitudinal wave features, practise v = fλ and echo problems, then take the Sound quiz.

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