Topic 4 - Waves And The Earth

Question 0

Ultrasound has a frequency higher than?

Answer 0

20,000 Hz

Question 1

What is partial reflection?

Answer 1

When a waves passes from one medium into another, some of the wave is reflected and some is transmitted and refracted

Question 2

Infrasound has a frequency less than?

Answer 2

20 Hz

Question 3

How is ultrasound useful?

Answer 3

It can be used for pre-natal scanning of a foetus the waves being pointed at the foetus and when it reaches the foetus some of it is reflected back and detected.

Sonar. Boats and submarines emit waves of ultrasound which reflect off things like other boats, the sea bed, and animals. The waves the reflect off the and are detected back at the boat. They time the delay between emitting the wave and detecting the reflection and they can calculate how far away the object is.

Animals such as bats and dolphins use it too sense their way around their environment.
Animals such as frogs insects and whales use it to communicate.

Question 4

Why can infrasound waves travel far?

Answer 4

Because they have long wavelengths and can diffract around objects easily.

Question 5

State 3 examples of applications of infrasound.

Answer 5

Tigers use it in their growls so they can be heard by rivals or mates from far away.
Elephants use it to communicate over long distances.
We can use it to detect meteor strikes and volcanic eruptions.

Question 6

A sonar pulse is sent out by a boat. It reflects of the sea bed and takes 10 seconds to return. The sped of sound through water is 1500m/s. Calculate how far away the sea bed is.

Answer 6

1500 x 10 = 15000

15000/2 = 7500 m

Question 7

What are the 4 layers of the earth?

Answer 7

Crust
Mantle
Outer core
Inner core

Question 8

Describe the cause of earthquakes using the worlds convection, plate, sudden, mantle

Answer 8

The crust is split up into sections which are called tectonic plates. In the mantle are convection currents that pull and push the tectonic plates. As the plates try to slide past each other there is a build up of stress. The stress is released in the sudden jerking of the plates which cause and earthquake.

Question 9

Are p waves longitudinal or transverse?

Answer 9

Longitudinal

Question 10

Are S waves transverse or longitudinal?

Answer 10

Transverse

Question 11

What substances can p waves travel through?

Answer 11

Any

Question 12

What substances can S waves travel though?

Answer 12

Solids not liquids or gases

Question 13

Are p waves fast or slow?

Answer 13

Fast

Question 14

Are S waves fast or slow?

Answer 14

Slow

Question 15

How do we know the earths outer core is a liquid?

Answer 15

Because p waves can travel through it but S waves can’t.

Question 16

What instrument is used to detect p waves and S waves?

Answer 16

Seismometer

Question 17

Which wave is the first tremor on the seismogram?

Answer 17

P wave

Question 18

How can you work out where the earthquake was from the time distance between the two waves?

Answer 18

You work out how far away it was from each seismometer then you draw a circle centred on the location of your seismometer with the distance you calculated as the radius. This is a distance arc. All the distance arc will cross at one place which is the epicentre of the earthquake. This method is called triangulation. It only works if you have three or more seismometers.