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Ultrasound (AQA GCSE Physics)
Revision Note
Ultrasound (HT 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
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