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GCSE Physics · key term
Sound with a frequency less than 20 Hz, below the usual range of human hearing.
Used by AQA, Edexcel and OCR
Specification 4.6.1.4 · Paper 2
Infrasound is sound with a frequency below 20 Hz, the lower limit of normal human hearing.
Revise: Sound wavesSound below 20 Hz is called infrasound; sound above 20 kHz is called ultrasound. These are still sound waves, even though their frequencies lie outside the normal human hearing range.
Specification 4.14P, 4.15P · Paper 1
Sound with a frequency of less than 20 hertz (Hz).
Revise: Infrasound DefinitionInfrasound is sound with a frequency of less than 20 Hz. For example, a 12 Hz sound wave is infrasound because 12 Hz is below the 20 Hz boundary.
Specification P5.1i · Paper 2 (Foundation), Paper 4 (Higher)
Sound with a frequency below about 20 Hz, which is normally below the human hearing range.
Use the strict boundary stated by Edexcel: infrasound has a frequency less than 20 Hz. A frequency of exactly 20 Hz is not less than 20 Hz.
Do not confuse frequency with amplitude. A sound is infrasound because its frequency is below 20 Hz, not because it is quiet.
Infrasound is still a sound wave even though humans usually cannot hear it.
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