P1.4 Waves And The Earth Flashcards
What is the frequency of ultrasound?
A wave with over 20000 Hz.
What are two uses of ultrasound?
Pre-natal scanning of a foetus
Sonar equipment
How does pre-natal scanning of a foetus work?
Ultrasound waves are reflected when they meet a different mediums boundary eg the skin of the foetus. The reflected waves are recorded to give an image of the child.
How does sonar equipment work?
The boat emits ultrasound waves which reflects off objects like marine animals, submarines and the sea bed. An on board computer then calculates how far away they are.
What is the frequency of infrasound?
Why can infrasound be useful?
It has long wavelengths and so can travel long distances and diffract easily around objects.
What is the formula linking wave speed, distance and time?
Wave speed = distance/time.
How do you calculate distance from an ultrasound source to an object?
Wave speed *time / 2 because the wave travels there and back.
How far away is a seabed from a ship if the ultrasound takes 4.5 second to travel there and back, and the speed of sound in seawater is 1520m/s?
Distance= 1520*4.5 -= 6480m/2 = 3420m
What are the four layers of the earth?
Crust
Mantle
Outer core
Inner core
What causes tectonic plates to move?
Convection currents in the mantle.
Why are earthquakes and tsunamis a problem?
They are very destructive and very hard to predict.
How do scientists learn more about the inner structure of the earth?
Seismometers all over the world detect seismic waves. If a seismometer in a certain area does or does not record certain types of seismic waves, we can find their path and where they did and didn’t travel.
What are the properties of p-waves?
They are longitudinal
They travel through solids and liquids
They are faster than s-waves
What are the properties of s-waves?
They are longitudinal
They only travel through solids
They are slower than p-waves.
