Sound Waves

This lesson covers the properties and behaviour of sound waves — as required by the Edexcel GCSE Physics specification (1PH0), Topic 4: Waves. You need to understand how sound is produced and transmitted, the factors affecting pitch and loudness, the human hearing range, and applications of ultrasound.

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How Sound Is Produced

Sound is produced by vibrations. When an object vibrates (e.g. a guitar string, a tuning fork, a loudspeaker cone), it causes the particles of the surrounding medium (usually air) to vibrate back and forth.

• The vibrating object pushes air molecules together, creating a region of compression (high pressure).
• It then pulls back, creating a region of rarefaction (low pressure).
• These alternating compressions and rarefactions travel outwards from the source as a longitudinal wave.

Key Facts

• Sound is a longitudinal wave — the particles vibrate parallel to the direction of energy transfer.
• Sound requires a medium to travel through — it cannot travel through a vacuum (empty space).
• This is because there are no particles in a vacuum to vibrate and pass the wave on.
• Sound can travel through solids, liquids, and gases.