AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Sound waves travelling through air are longitudinal.
Full specification wording
Transverse and longitudinal waves: Sound waves travelling through air are longitudinal.
Sound is a mechanical wave carried by the vibration of the particles of a medium.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 4 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Sound is a mechanical wave carried by the vibration of the particles of a medium. A loudspeaker cone moving outwards pushes the air molecules in front of it together, creating a compression; as it moves back it leaves them further apart, creating a rarefaction. The molecules oscillate backwards and forwards along the direction the sound travels, so the wave is longitudinal. Because it needs particles, sound cannot cross a vacuum, unlike light. Sound in air travels at roughly 330 m/s, around a million times slower than light, which is why thunder arrives seconds after the flash. Sound travels faster in solids and liquids, where the particles are closer together. The greater the amplitude of the vibration the louder the sound, while the greater the frequency the higher the pitch.
What earns the marks
- Stating that the air particles oscillate parallel to the direction of energy transfer.
- Describing the series of compressions and rarefactions produced.
- Stating that sound needs a medium and cannot travel through a vacuum.
- Comparing the speed of sound in air, about 330 m/s, with the speed of light.
Common mistakes and how to put them right
Saying sound travels more slowly in solids than in air.
Describing sound as an electromagnetic wave.
Claiming the air itself moves from the loudspeaker to the listener's ear.
Saying sound travels through a vacuum more quickly because there is nothing in the way.
Exam tips
- In light and sound comparisons, cover type, medium, speed and wavelength to reach the top level.
- Quote a value for the speed of sound in air; an approximate 330 m/s to 340 m/s is accepted.
- Say 'parallel to the direction of energy transfer' rather than 'in the same direction'.
Try the lesson
The start of the Transverse and longitudinal waves: Sound waves travelling through air are longitudinal. lesson, made from checked teaching notes for this specification point.
Have a go first
Which type of wave is a sound wave travelling through air?
Listen
Sound is a mechanical wave carried by the vibration of the particles of a medium. A loudspeaker cone moving outwards pushes the air molecules in front of it together, creating a compression; as it moves back it leaves them further apart, creating a rarefaction. The molecules oscillate backwards and forwards along the direction the sound travels, so the wave is longitudinal. Because it needs particles, sound cannot cross a vacuum, unlike light. Sound in air travels at roughly 330 m/s, around a million times slower than light, which is why thunder arrives seconds after the flash. Sound travels faster in solids and liquids, where the particles are closer together. The greater the amplitude of the vibration the louder the sound, while the greater the frequency the higher the pitch. A strong answer earns marks for these points. stating that the air particles oscillate parallel to the direction of energy transfer. describing the series of compressions and rarefactions produced. stating that sound needs a medium and cannot travel through a vacuum. comparing the speed of sound in air, about 330 m/s, with the speed of light. Exam tip: In light and sound comparisons, cover type, medium, speed and wavelength to reach the top level.
Key words
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sound waves
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longitudinal
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compressions and rarefactions
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medium required
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See every definition
- sound waves
- A mechanical wave carried by the vibration of the particles of a medium, travelling through air as a longitudinal wave.
- longitudinal
- Describes a wave in which the molecules oscillate backwards and forwards along the direction the sound travels.
- compressions and rarefactions
- A loudspeaker cone moving outwards pushes the air molecules in front of it together, creating a compression; as it moves back it leaves them further apart, creating a rarefaction.
- medium required
- Because it needs particles, sound cannot cross a vacuum, unlike light.
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