Properties of waves and Structure of the Earth

Question 1

3 main characteristics of primary waves

Answer 1

• Longitudinal waves
• Travel quickly (faster than S waves)
• Travel through solids and liquids

Question 2

3 main characteristics of secondary waves

Answer 2

• Transverse waves
• Travel slower than P waves
• Travel through solids

Question 3

4 main characteristics of surface waves

Answer 3

• 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

Question 4

Example of transverse waves

Answer 4

Light waves

Question 5

Example of longitudinal waves

Answer 5

Sound waves

Question 6

What is a plane wave?

Answer 6

Constant-frequency wave whose wavefronts are infinite parallel planes of constant peak-to-peak amplitude

Question 7

What is a transverse wave?

Answer 7

Waves where the direction of vibration of particles or fields is perpendicular to the direction in which the wave travels

Question 8

What are the only waves that undergo polarisation?

Answer 8

Transverse

Question 9

What is a longitudinal wave?

Answer 9

Waves where direction of vibration of particles is parallel to direction in which the wave travels

Question 10

When does refraction occur?

Answer 10

When a wave passes across a boundary at which the wave speed changes

Question 11

What has more of an impact on speed of transverse wave than density?

Answer 11

Rigidity

Question 12

What happens when waves strike a plane (flat) barrier?

Answer 12

Waves are reflected

Question 13

What two angles will be equal if waves are reflected?

Answer 13

Angle of incidence and angle of reflection

Question 14

Definition of refraction

Answer 14

Change in direction of a wave at the boundary between two materials caused by a change in speed

Question 15

Angles at refraction when light moves from more optically dense material (e.g. water) to less optically dense material (e.g. air)

Answer 15

Incident angle is less than critical angle causing the ray to refraction (bend away from angle). This is known as angle of refraction

Question 16

Angles that show why light ray can pass along surface of boundary

Answer 16

Incident angle equal to critical angle

Question 17

Angles that show total internal reflection when light is shone in water

Answer 17

Incident angle greater than critical angle so ray reflected back into water

Question 18

Uses of total internal refraction

Answer 18

• Optical fibres

- Endoscopes

Question 19

How are earthquakes caused?

Answer 19

Stresses in Earth build up over time which then break to relieve stresses which releases a lot of energy

Question 20

What will happen to waves in the mantle?

Answer 20

Density and stiffness will increase but rigidity makes P and S waves travel faster causing them to refraction and change direction

Question 21

What happens to the waves inside the core?

Answer 21

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

Question 22

What happens to waves that pass through inner core?

Answer 22

They refract

Question 23

What happens to waves that pass from inner core back into the mantle?

Answer 23

They refract again

Question 24

Waves that travel through crust (solid), mantle (solid), outer core (liquid) and inner core (solid)

Answer 24

• Crust = P, S and surface waves
• Mantle = P and S waves
• Outer Core = P waves
• Inner Core = P waves

Question 25

What does existence of S wave shadow zones show?

Answer 25

Exist due to liquid outer core so there must be a molten layer which gives evidence to its size

Question 26

What does size of P wave shadow zones show?

Answer 26

Amount of refraction at core which gives evidence for its density/rigidity

Question 27

What are seismograms used for?

Answer 27

Locating the epicentre of an earthquake

Question 28

Why don’t all monitoring stations receive seismic waves?

Answer 28

Shadow zones

Question 29

What is reflection?

Answer 29

Wave is reflected if it strikes a plane (flat) barrier

Question 30

What is refraction?

Answer 30

Change in direction of a wave at the boundary between 2 materials which is caused by a change in speed

Question 31

When does Total Internal Reflection occur?

Answer 31

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

Question 32

2 uses of Total Internal Reflection

Answer 32

• Optical fibres

- Endoscope

Question 33

What does velocity of P and S waves depend upon?

Answer 33

• Density of rock/material (higher density, wave travels slower)
• Rigidity of material (more rigid/stiff, wave travels more quickly)