GCSE Physics · Edexcel 1PH0 · Topic 4C
Sound, ultrasound and seismic waves
Key points
- Sound waves are longitudinal and need a medium. In solids, sound makes particles vibrate and can make objects such as the eardrum vibrate.
- Human hearing range is about 20 Hz to 20 000 Hz. Higher frequency means higher pitch; larger amplitude means louder.
- Ultrasound (above 20 kHz) is partly reflected at boundaries between materials. The time for echoes gives depth: distance = . Used in pre-natal scans and sonar.
- Infrasound (below 20 Hz) is used to study animals and Earth's interior.
- P-waves are longitudinal, faster and travel through solids and liquids. S-waves are transverse, slower and only travel through solids.
- The S-wave shadow zone shows the Earth's outer core is liquid; seismometers in different places help locate earthquakes.
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Sound is a longitudinal wave that needs a medium, and its high- and low-frequency relatives let us scan unborn babies, map the sea floor and work out the structure of the Earth. This sub-topic applies wave ideas to these real uses.
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