4.6.1.5 Waves for Detection and Exploration (physics only) (HT only)

Question 1

How can ultrasound be used to determine distance?

Answer 1

use equation s = v x t

Question 2

Ultrasound:

Answer 2

ultrasound is sound waves with a frequency higher that the upper limit of human hearing (so at least 20,000 Hz)

Question 3

Uses of ultrasound + explanation:

Answer 3

Medical and industrial imaging

• ultrasound waves are partially reflected when they meet a boundary between 2 different media (so 2 different densities
• the time taken for the reflections to reach a detector can be used to determine how far away such a boundary is
• this means that ultrasound scanners can produce images of internal organs e.g. the kidney and heart - works for any organ not surrounded by bone
• can also be used to see image of foetus
• ultrasound can be used to detect hidden defects or problems with a weld

Question 4

Why is ultrasound safer than X-rays?

Answer 4

ultrasound safer than X-rays as it does not cause mutations and so doesn’t increase the rick of cancer

Question 5

Seismic waves:

Answer 5

waves produced by an earthquake

Question 6

Internal structure of the earth:

Answer 6

• outside of the earth is the solid crust
  
  • crust is very thin with a maximum depth of approx. 50km
• under crust is mantel
  
  • mantel is solid
  • however, parts of the upper mantel can flow very slowly but mantel is still considered a solid
• outer core is a liquid
• inner core is a solid

Question 7

How can scientists observe the interior of the Earth?

Answer 7

• scientists cannot directly observe the interior of the Earth - even the deepest mines only go few km’s into crust
• scientists know the interior of the Earth has this structure because of earthquakes
  
  • earthquakes cause seismic waves which carry energy away from the earthquake
  • these seismic waves then pass through the earth and can be detected by seismometers in different countries
  • patterns on these waves can give us information about the interior of the wave

Question 8

Why does an earthquake happen?

Answer 8

an earthquake happens due to sudden movement between the tectonic plates on the Earth’s crust

Question 9

What is the path of seismic waves and how does it allow scientists to learn about the structure of the interior of the Earth?

Answer 9

• seismometers on the Earth’s surface can detect seismic waves after they have passed through the Earth after an earthquake
• seismic waves travel in curved paths due to density changes in the Earth
• S-waves detected in mantel
• large parts of Earth’s interior where S-waves not detected (S-wave shadow zone)
  
  • due to the fact that S-waves cannot pass through a liquid
  • so cannot travel through outer core - shows that the outer core is liquid
  • told scientists that the Earth must contain a liquid core or at least a core made partially from liquid material
• P-waves can pass through mantel, outer core and inner core
• large parts of Earth where P-waves cannot be detected (P-wave shadow zones)
  
  • due to fact the P-wave travel faster in solids than liquids which means that the P-wave slow down as they enter the liquid outer core which causes them to refract towards the normal
  • P-waves also refract when they leave outer core - indicates density of earth changed at dif depths (presence of boundaries)
  • this confirms that the outer core is a liquid
  • as you go deeper into mantel speed increases (rock is probably denser)
• sometimes faint P-waves can be detected in P-wave shadow zone
  
  • used by scientists to show that the Earth also contains a solid inner core

Question 10

How have scientists used seismic waves to determine the thickness of the different parts of the Earth’s interior?

Answer 10

• scientist have measured seismic waves from 1000s of earthquakes
• used these to work out the thickness of the crust, mantel, outer and inner cores

Question 11

2 main types of seismic waves:

Answer 11

• P - Waves (primary waves)
• S - Waves (secondary waves)

Question 12

What type of waves are P-waves?

Answer 12

longitudinal waves

Question 13

What states of matter can P-waves pass through?

Answer 13

can pass through solid and liquids

Question 14

How fast do P-waves travel?

Answer 14

• P-waves travels faster than S-waves
• P-waves travel at different speeds in solids and liquids

Question 15

What parts of Earths interior can P-waves travel through?

Answer 15

• crust
• mantel
• outer core
• inner core

Question 16

What type of waves are S - waves?

Answer 16

transverse waves

Question 17

What states of matter can S - waves pass through?

Answer 17

solid

Question 18

What parts of Earths interior can S-waves travel through?

Answer 18

• crust
• mantel

Question 19

Echo sounding:

Answer 19

using high frequency sound waves - echo sounding is used to detect objects in deep water and measure water depth

Question 20

What parts of the Earths interior can S-waves not travel through?

Answer 20

cannot travel through outer core as it is liquid and S-waves cannot travel through a liquid