Topic 3.2: Ultrasound, Infrasound and Seismic Waves Flashcards
What is ultrasound?
Sound with frequencies higher than 20,000 Hz (above the range of human hearing)
Describe 2 uses for ultrasound
Medical Imaging (scanning of a foetus)
- Waves pass through the body, when they reach a boundary between two different media (fluid in womb and skin of foetus) they are reflected back and detected
- Exact timing and distribution of these echoes are processed by a computer, producing an image of the foetus
Industrial Imaging (finding flaws in materials)
- When there is a flaw/crack in the object, the waves will be reflected sooner than when the waves are reflected by the far side of the material
Describe 2 uses for infrasound
Some animals such as elephants and whales communicate using infrasound, so scientists can track them for conservation purposes
Scientists can predict events by monitoring infrasound produced by volcanoes, avalanches and earthquakes
What is infrasound?
Sound with frequencies lower than 20 Hz (below the range of human hearing)
What are seismic waves detected by?
Seismometers
What waves do earthquakes and explosions produce?
Seismic waves
What are the properties of P-waves?
- Longitudinal
- Travel through solids and liquids
- Faster than S-waves
What are the properties of S-waves?
- Transverse
- Only travel through solids (shows us that the Earth has a liquid outer core)
- Slower than P-waves
Why do seismic waves have curved paths through the Earth?
- When they reach a boundary between different layers with different densities, some waves are absorbed and some are refracted
- These refracted waves change speed gradually in the different medium resulting in a curved path
Explain how vibrations from earthquakes may be used to study the core of the Earth
explanation linking:
- use seismometers
- some seismic waves are transverse and longitudinal
- P-waves can go through solids and liquids
- S-waves can’t travel through liquid. So, detected shadow zones show that part of the earth’s core must be liquid
