CIE IGCSE Physics

Revision Notes

3.4.1 Sound & Ultrasound

Sound

  • Sound waves consist of vibrating molecules. They are a type of longitudinal wave

 

longitudinal-wave-definition, IGCSE & GCSE Physics revision notes

Sound waves are longitudinal: the molecules vibrate in the same direction as the energy transfer

  • Sound waves require a medium to travel through
    If there are no molecules (e.g. in a vacuum) then the sound can’t travel
  • The Loudness of a sound is related to the wave’s amplitude
    (Greater amplitude = louder sound)
  • The Pitch of a sound is related to the frequency
    (Greater frequency = higher pitch)
  • As with all waves, sound waves can be reflected
    The reflection of a sound wave is called an echo
Extended Only

Compression & Rarefaction

  • Longitudinal waves consist of compression and rarefactions:
    • A compression is a place where the molecules are bunched together
    • A rarefaction is a place where the molecules are spread out

 

Compressions and rarefactions, IGCSE & GCSE Physics revision notes

Diagram showing the compressions and rarefactions of longitudinal waves

Ultrasound

  • Humans can hear sounds between about 20 Hz and 20 000 Hz in frequency (although this range decreases with age)

 

Range of human hearing, IGCSE & GCSE Physics revision notes

Humans can hear sounds between 20 and 20 000 Hz

 

  • Ultrasound is the name given to sound waves with a frequency greater than 20 000 Hz

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