Ultrasound (AQA GCSE Physics): Revision Note

Ultrasound

Higher Tier Only

• Ultrasound is defined as:

  Sound waves with a frequency above the human hearing range of 20 000 Hz

• The human ear can hear frequencies between 20 Hz and 20 000 Hz

The human ear can detect sounds between around 20 and 20 000 Hz in frequency with a peak sensitivity at around 4000 Hz

• When meeting a boundary between two media ultrasound may be:

  • Partially reflected

  • Partially transmitted

  • Partially absorbed

• The percentage that is reflected or transmitted depends on the two media at the boundary

  • An air and glass boundary will have different percentages compared to an air and wall boundary

• The percentage of the wave reflected is greatest when the difference in speed of sound between the media is large

  • For example, when sound in air hits a brick boundary, most of the sound is reflected because waves travel much faster in brick than in air