# Physics 3- Waves + Earthquakes

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Define transverse waves
Oscillations of waves at 90 degrees to direction
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Define longitudinal waves
Oscillations in the same direction as direction of travel
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Define Wavelength
Crest to crest measurement, repeating distance
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Define Frequency
Waves per second
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What is frequency measured in?
Hz
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Define amplitude
Middle of wave to crest measurement
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IN waves, the higher the amplitude the higher the what?
Energy
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What is reflection?
Waves striking a barrier and reflecting off of it
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How do waves act with a curved, bioconcave barrier?
They converge at a certain point
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What is the angle of incidence?
The angle at which the wave hits the plane/barrier
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What is the angle of incidence equal to?
Angle of reflection
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What is refraction?
Where the wave changes direction at the boundary between two materials
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What is refraction in terms of wave action?
A change in speed
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How do waves react when moving through shallow water?
Frequency remains the same, wavelength decreases
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How do waves react in deeper water?
Speed increases, direction change AWAY from normal
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Are waves faster in deep or shallow water?
Deeper
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How do waves react when passing between materials of different optical densities?
They refract
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How do waves react when passing from air to glass?
Slow down, bending towards the normal
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How do waves react when passing from glass to air?
Speed up, bending away from normal?
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Define Total Internal Reflection?
The wave is reflected back into the medium.
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When does total internal reflection occur?
When the wave is moving more from a more optically dense material to a less optically dense material.
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Describe total internal reflection
Increasing the incidence angle pushes the refraction angle closer 90 degrees. It reaches the critical angle (r =90) where it refracts along the boundary, incident angle above the critical angle makes the wave reflect back into the material
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How is total internal reflection be used?
Optical fibres, using infrared light- Internet, phone and cable TV
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How can optical fibres be used in the medical field?
Endoscopy, bundled optical fibres into body, light directed down the bent fibres, illuminates chosen area.
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How are seismic waves produced?
Built up energy releases seismic waves when a plate stress ruptures
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What are the seismic waves?
P, S and Surface Waves
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How is an earthquake produced?
The ruptured stress releases energy from either side of the fault, releasing P, S and surface waves which create an earthquake
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Describe a P wave
Primary wave,faster, arriving first. Longitudinal wave that can travel through solids and liquids.
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Describe an S wave
Secondary waves, slower, arriving second. Transverse waves that can only travel through liquids
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Describe a surface wave
Slowest with the highest amplitude. Formed from a combination of P and S waves that travels along the earth's crust. These waves are the damaging ones, causing buildings to fall etc.
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What does seismic wave speed depend on?
The physical properties of the rock
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How can rock type be found using seismic waves?
By measuring velocity of the waves.
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Name, from outside to inside, the structure of the earth
Crust, mantle, outer core and inner core
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What parts of the earth are made up of solid rock?
The Mantle and inner core
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What is the outer core made of?
Liquid rock
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Which kind of waves can travel through the whole earth?
P waves
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Where can S waves no longer be found in the earth?
The outer core
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What does the velocity of a wave depend on and how do these things effect it?
A higher density means the wave travels slower, a more rigid material the wave travels faster
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Describe the speed of P waves from the mantle to the core
The iron core has a greater density than the mantle, so the wave slows down
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How does the speed change as the wave travels through the core?
Speed increases with depth, and when crossing into the more rigid core
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Which has more effect, rigidity or density?
Rigidity
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Describe the wave speed in the mantle and why it happens
The mantle becomes both more rigid and dense with depth, rigidity wins out and the wave speeds up with depth
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How does a wave speed change in the mantle effect the direction of the wave?
It refracts and changes direction
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Describe wave refraction in the mantle
Curved waves- the bottom edge travels faster, overtaking the top edge = BENDING UPWARDS. P+ S waves do this
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Describe wave speed/direction inside the core
The waves slow down, refracting at the boundary. The waves curve gradually, speeding up as they travel down (core more rigid deeper)
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How much do the waves refract inside the core and what does this tell us about the speed?
Only slightly, speed only changes a little bit
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Describe wave action in the inner core
The waves refract again, refraction passes back through mantle
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How could one estimate the size of the liquid core?
Measuring the P +S waves at different points across the world
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How do P+S waves travel initially?
In all directions outwards from the epicentre
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How does this change?
They are refracted travelling from the epicentre and follow arced directions
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Why are there wave shadow zones on the opposite side of the earth form the epicentre
There are no S waves in or through the liquid outer core
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Two, smaller than S wave shadow zone. Refraction leaves gaps between wave arcs
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How can the radius of the liquid core be found?
The angle of wave disappearance, there is a density change between the solid mantle and the liquid core
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How can the amount of refraction at the core be found?
Measuring the size of the shadow zone
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What can be found from the amount of refraction at the core?
The density of the rock
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What can device can be used to find the epicentre?
Seismogram
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What does the distance between waves show?
How far the epicentre is from the seismogram
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Why do seismograms in some places not pick up any waves?
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## Other cards in this set

### Card 2

#### Front

Define longitudinal waves

#### Back

Oscillations in the same direction as direction of travel

### Card 3

#### Front

Define Wavelength

Define Frequency

### Card 5

#### Front

What is frequency measured in?