Waves And The Earth Flashcards
What is ultra sound
Sound with frequencies higher than 20000hz which is beyond the range of human hearing
What happens when ultrasound hits a boundary
Some of the wave is reflected and some is refracted this partial reflection
This means when you point ultrasound at an object some of it will always be reflected back
How is ultrasound used in prenatal scanning of a foetus
The waves can pass through the body but when they reach a boundary between two different mediums some of the wave is reflected back and detected
The more dens the medium the more ultrasound reflected
The timings and distribution of the waves detected are processed by a computer to make a video image
How is ultrasound used in sonar
Boat and submarine use sonar to detect things in the water around them
They emit ultrasound waves that reflect off things around them and can be detected back at the boat
Computers on board calculate the speed of the wave and the time it takes to come back so they can work out how far away the object is
Animals like bats and dolphins use this in a similar way
What is infrasound
Sound with frequencies less than 20hz that can’t be heard by humans
They have long wavelengths so can travel long distances easily
What are the uses of infrasound
Elephants use it to communicate over long distances
Tigers use it to communicate to rivals or mates far away
Microphones detecting infrasound can be used to monitor animal movement
Meteor strikes and volcanic eruptions produce infrasound which allows them to be detected from a long way away
Wave speed =
Distance / time
Remember to half the value when finding ultrasound distance
What is the structure of the earth
It's spherical There's a thin crust A mantle has the properties of a solid but can slowly flow in convection currents because of radioactive decay producing heat The outer core is solid The inner core is liquid
What are tectonic plates
They are big parts of the earths crust which float on the mantle
Convection currents cause them to move which can cause them to collide or slide over each other at plate boundaries
Why is it difficult to predict earthquakes
They’re very unpredictable and can happen at any time
We can look at patterns of previous earthquakes but it’s not a very accurate method
What are p waves
Longitudinal waves that travel through liquids and solids faster than S waves
What are S waves
Transverse waves that travel only through solids slower than p waves
What are seismic waves
They’re produced by earthquakes in the form of s or p wav
What happens when seismic waves hit boundaries
Some will be reflected but mostly they refract and the slight changes in density cause a curved path but when the properties change quickly it causes kinks
Why observing where seismic waves are reflected and refracted scientists can work out where the properties of the earth change dramatically
What is a seismometer
It collects the seismic waves and records them p and S waves travel at different speeds so there is usually two different peaks on the graph and the distance between the two shows how far apart the p and S waves are
