Properties of waves and Structure of the Earth Flashcards
3 main characteristics of primary waves
- Longitudinal waves
- Travel quickly (faster than S waves)
- Travel through solids and liquids
3 main characteristics of secondary waves
- Transverse waves
- Travel slower than P waves
- Travel through solids
4 main characteristics of surface waves
- Higher amplitude than P and S waves
- Usually cause buildings to knock down
- Formed by combination of P and S waves
- Slowest of 3 waves
Example of transverse waves
Light waves
Example of longitudinal waves
Sound waves
What is a plane wave?
Constant-frequency wave whose wavefronts are infinite parallel planes of constant peak-to-peak amplitude
What is a transverse wave?
Waves where the direction of vibration of particles or fields is perpendicular to the direction in which the wave travels
What are the only waves that undergo polarisation?
Transverse
What is a longitudinal wave?
Waves where direction of vibration of particles is parallel to direction in which the wave travels
When does refraction occur?
When a wave passes across a boundary at which the wave speed changes
What has more of an impact on speed of transverse wave than density?
Rigidity
What happens when waves strike a plane (flat) barrier?
Waves are reflected
What two angles will be equal if waves are reflected?
Angle of incidence and angle of reflection
Definition of refraction
Change in direction of a wave at the boundary between two materials caused by a change in speed
Angles at refraction when light moves from more optically dense material (e.g. water) to less optically dense material (e.g. air)
Incident angle is less than critical angle causing the ray to refraction (bend away from angle). This is known as angle of refraction
Angles that show why light ray can pass along surface of boundary
Incident angle equal to critical angle
Angles that show total internal reflection when light is shone in water
Incident angle greater than critical angle so ray reflected back into water
Uses of total internal refraction
- Optical fibres
- Endoscopes
How are earthquakes caused?
Stresses in Earth build up over time which then break to relieve stresses which releases a lot of energy
What will happen to waves in the mantle?
Density and stiffness will increase but rigidity makes P and S waves travel faster causing them to refraction and change direction
What happens to the waves inside the core?
They refract at core-mantle boundary as they slow down. Inside core they gradually curve as they deeper they get, the faster they travel because core is more rigid. Don’t refraction much though as speed doesn’t change much
What happens to waves that pass through inner core?
They refract
What happens to waves that pass from inner core back into the mantle?
They refract again
Waves that travel through crust (solid), mantle (solid), outer core (liquid) and inner core (solid)
- Crust = P, S and surface waves
- Mantle = P and S waves
- Outer Core = P waves
- Inner Core = P waves
What does existence of S wave shadow zones show?
Exist due to liquid outer core so there must be a molten layer which gives evidence to its size
What does size of P wave shadow zones show?
Amount of refraction at core which gives evidence for its density/rigidity
What are seismograms used for?
Locating the epicentre of an earthquake
Why don’t all monitoring stations receive seismic waves?
Shadow zones
What is reflection?
Wave is reflected if it strikes a plane (flat) barrier
What is refraction?
Change in direction of a wave at the boundary between 2 materials which is caused by a change in speed
When does Total Internal Reflection occur?
When light moves from a more optically dense material (e.g. water) to a less optically dense material (e.g. air) causing a change in speed
2 uses of Total Internal Reflection
- Optical fibres
- Endoscope
What does velocity of P and S waves depend upon?
- Density of rock/material (higher density, wave travels slower)
- Rigidity of material (more rigid/stiff, wave travels more quickly)
