Sound And Seismic Waves Flashcards
What are transverse waves
The movement of a transverse wave is at a right angle to the direction in which the energy is travelling
What are longitudinal waves
The movement of a longitudinal wave is in the same direction as which the energy is travelling in
What is frequency
The number of waves per second
What is the wave equation
Wave speed = frequency X wavelength
What is amplitude
Maximum displacement of the wave from the point of equilibrium
What is the wavelength
The distance from trough to trough
The frequency of a sound produced by a guitar string is 440Hz. What does this mean
440 vibrations per second
What does ultrasound mean
Any frequency over 20,000Hz
What is infrasound
Any frequency under 20Hz
What happens to the particles in sound
The particles vibrate back and fort and collide with eachother, passing the energy on. The particles vibrate in the same direction as the energy travels.
Uses of ultrasound
- frequency above 20,000Hz
- commonly used to create images medically
- is based on the reflection and transmission of a wave at a boundary
- higher frequencies provide better quality, but are more readily absorbed by the skin
- transmitted from the probe through the gel into the body
Used of infrasound
- frequency below 20Hz
- is detected using a microphone
- scientists can use infrasound to track the passage of meteors through the atmosphere
- infrasonic sound can be the result of a volcanic eruption
- elephants and giraffes use infrasound to communicate between herds over long distances
Echolocation
- animals such as bats and Dolphins
- use high frequency sounds to create a mental image of their location
- emit calls to the environment and listen to the echoes of those calls that return from various objects near them
How is infrasound used for tracking animals
The frequency can be detected using machines and vibrations caused by their movement to locate animals
What is sonar
It is a technique that uses sound propagation
What is sonar used for
For navigating, communicating or detecting objects on or under the surface of the water
How does crack detection work
A wave is reflected from the bottom of the sample and is then reflected from the flaw to the transmitter/receiver
What is crack detection
Sonar is used with time taken to receive an echo being measured. It is used to detect cracks and defects which weakens metal, bars and pipes
What are primary waves
Longitudinal waves
What are secondary waves
Transverse waves
What do primary waves travel through
Solids and liquids
What do secondary waves go through
Solids only
What is the crust
Relatively think and rocky
What is the inner core like
Made from solid nickel and iron
What is the outer core like
Made from liquid nickel and iron
What is the mantle like
Has properties of a solid, but can flow very slowly
Explain why we think Earth had a liquid core which contains a solid inner core?
- Earth gives out both P and S waves
- S waves cannot travel through a liquid
- No S waves pass through the middle of the Earth
- P waves can travel through the liquid core and are detected
- however, their direction is refracted, meaning there is a different material in the centre of the core, such a solid
What are the two main types of wave
Transverse
Longitudinal
A scientist can work out the location of an earthquake by:
- using a seismometer to pick up vibrations
- calculating the time difference between the arrival of the s and p waves received to find how far the source is away
- comparing the data from atleast 3 different seismometers to find the epicentre
Why is it hard to predict when and where an earthquake will occur
They tend to occur along fault lines, but it is hard to predict where along it the pressure will build up. There are no known precursors for earthquakes
Where is the epicentre
The place of origin of the earthquake
Where is the focus
Directly above the origin of the earthquake
How is ultrasound used to create medical images
- a pulse is sent of ultrasound from the probe
- the gel between the probe and skin allows the ultrasound to travel through the body
- then some of the ultrasound waves reflect from the boundary, which in this case is the baby’s head
- the time between sending the pulse and detecting reflecting waves is used to calculate the depth / distance to the baby
