P12: The Nature Of Waves (Y10 - Summer 2)

Question 1

🟢 What is the period of an oscillation?

Answer 1

The period of an oscillation is the time it takes for one full oscillation to happen.

Question 2

🟢 What is a wave?

Answer 2

A wave is a series of oscillations that travel from one place to another, transferring energy all while without transferring matter.

Question 3

🟢 What is a transverse wave? (+ Examples of them)

Answer 3

In a transverse wave, the direction of oscillation is perpendicular to the direction of wave motion. An example of transverse waves are the waves in a rope, and the ripples on the surfave of water, because the vibrations (oscillations) move up and down or from side to side.

(All electromagnetic waves are transverse waves)

(Displacement (m) is on the Y-Axis, while Distance (m) is on the X-Axis)

Question 4

🟢 What are Longitudinal Waves

Answer 4

Sound waves travelling through air are longitudinal waves. When an object vibrates in air, it makes the air around it vibrate as it pushes and pulls on the air. The oscillations (compressions and rarefactions) that travel through the air are sound waves. The oscillations are along the direction in which the wave travels.

The oscillations of a longitudinal wave are parallel to the direction in which the waves transfer energy.

Mechanical waves can be transverse or longitudinal.

Question 5

🟢 What is Wavelength, Amplitude, Peak/Crest, and Trough on a Transverse Wave

Answer 5

Wavelength - The length of one wave to another (measure from the very highest point of each wave)

Amplitude - The height of a wave taken from the top/bottom of the wave, to the X-Axis

Peak/Crest - The very top of a wave

Trough - The very bottom of a wave

Question 6

🟢 What is a longditudinal wave and how is sound an example of a longitudinal wave

Answer 6

In a longditudinal wave, the direction of oscillation is parallel to the direction of wave motion. This means that sound waves for example, are longitudinal waves, as when an object vibrates in the air, it makes the around it vibrate as it puhses and pulls on the air, meaning the oscillations at travel through the air are sound waves.

(Particle motion is up on the Y-Axis, against the Direction of Propagation (Wave Motion) on the X-Axis)

Question 7

🟢 What is Frequency in Waves and the Equation for the Period

Answer 7

The number of waves passing a fixed point every second is called the frequency of the waves.

The unit for frequency is the hertz (Hz). For the waves on the rope, one wave vrest passing each second is equal to a frequency of 1 Hz.

The period of a wave is the time taken for each wave to pass a fixed point. For waves of frequency (s), the period (T) is given by the equation:

period, T (seconds, s) = 1 / Frequency, f (hertz, Hz)

Question 8

🟢 What is the Speed of Waves (+Equation for Wave Speed)

Answer 8

The speed of the waves is the distance travelled by each wave every second through a medium. Energy is transferred by the waves at this speed.

For waves of constant frequency, the speed of the waves depends on the frequency and the wavelength as follows:

Waves speed, v (m/s) = Frequency, f (Hz) x Wavelength, λ (m)

Question 9

🟢 Practice Question: Suppose the frequency of the waves is 3 Hz and the wavelength of the waves is 4.0m

Work out the speed of the surfer.

Answer 9

• At this frequency, three wave crests pass a fixed point once every second (because the frequency is 3 Hz)
• The surfer therefore moves forward a distance of three wavelength every second, which us 3 x 4.0m = 12m.

So the speed of the surfer is 12m/s.

This speed is equal to the frequency x the wavelength of the waves.

Question 10

🟢 How can you measure the speed of sound in air for example

Answer 10

If your friend bangs two cymbals together, you will see them crash together straightaway, but you won’t hear them straightway. The crashing sound will be delayed because sound travels much slower than light, espcially over futher distances. Usimag stopwatch to time the interval between seeing the impact and hearing the sound. Repeat the test several times to get an average value of the time interval.

Calculate the speed of sound in air using the equation:

Speed = Distance/Time Taken

Question 11

🟢 What is Compression and Rarefaction

Answer 11

Compression - When the waves are tightly packed together in a small area

Rarefaction - When the waves are widely spread out over a wide area

Question 12

🟢 What is the Law of Reflection

Answer 12

Angle of Incidence (°) = Angle of Reflection (°)

The reflected waves move away from the barrier at an equal angle to the incident waves.

Question 13

🟢 When any wave (e.g light) enters a denser medium, it will bend _____ from the normal.

When any wave (e.g light) enters a less dense medium, it will bend _____ from the normal.

Answer 13

When any wave (e.g light) enters a denser medium, it will bend towards the normal.

When any wave (e.g light) enters a less dense medium, it will bend away from the normal.

Question 14

🟢 What happens when light waves come from an angle to normal and what happens when light is parallel to the normal

Answer 14

Here, the waves hit the boundary at an angle. The waves refract.

Here, the waves hit the boundary straight on, at no angle. These waves do not refract.

Question 15

🟢 What happens to somes waves that are not reflected?

Answer 15

Waves can be absorbed:

• The material will gain energy from the waves. This will heat the material as its thermal energy store increases.
• As waves travel through a substance, the amplitude of the waves gradually decrease as the substance absorbs some of the waves’ energy

Waves can be transmitted through material:

-Waves can also travel through a material, therefore the waves are ‘transmitted’ by the material (this happens if they are not absorbed)

Question 16

🟢 What happens to waves when they refract at an angle and what happens when there is no angle

Answer 16

Refraction at an angle causes a wave to:

• Change speed
• Change direction
• Chnage wavelength

If there is no angle, the waves do not refract.

Question 17

🟢 What is the reflection of waves

Answer 17

Reflection of waves can be investigated using the ripple tank. Each ripple is called a wavefront because it is the front of each wave as it travels across the water surface. Plane (straight) waves, produced by repeatedly dipping the long edge of a ruler in water, are directed at a metal barrier im the water. These waves are called the incident waves, and the ones reflected are called reflected waves.

The incident wave is reflected by the barrier.

Question 18

🟢 How to test reflection

Answer 18

Use a ruler to create and direct plane waves at a straight barrier. Find out if the reflected waves are always at the same angle to the barroer as the incident waves. You could align a second rulee with the reflected waves and measure the angle of each ruler to the barrier. Repeat the test for different angles

Safety: Mop up any water spillages

Question 19

🟢 What is the refraction of waves

Answer 19

Refraction of waves is the change of direction in which they are travelling when they cross a boundary between one medium and another medium. You can see this in a ripple tank when water waves cross a boundary between deep and shallow water. Plane waves directed at a non-zero angle to the boundary change direction as they cross the boundary.

Question 20

🟢 How to test refraction

Answer 20

Use a vibrating beam to create plane waves continuously in a ripple tamk containing a transparent plastic plate.

Arrange the plate so that the waves cross a boundary between deep and shallow water. The water over the playe needs to be very shallowe.

At a non-zero angle to a boundary, the waves change their speed and direction when they cross the boundary. Find out if plane waves change direction towards or away from the boundary when they cross from deep to shallow water.

Perpendicular to aboundary (at normal incidence), the waves cross the boundary without changing direction. However, their speed changes.

-Find out if the waves travel slower or faster when they cross the boundary.

Safety: Mop up any water spillages.

Question 21

🟢 What happens in refraction

Answer 21

When plane waves cross a boundary at a nom-zero angle to the boundary, each wavefrint experiences a chnage in speed and direction.

Wavefronts move slowly after they habe crossed the boundary. So the refracted wavefronts are closer together and are at a smaller angle to the boundary than the incident wavefronts.

The revracted waves and the incident waves have the same frequency, butbthey travel at different speeds, so yhey have differeny wavelengths.

Question 22

🟢 Why are not all waves reflected from materials

Answer 22

When a wave is directed, some or all the wave may be reflected at the surface. What happens is dependant on the wavelength of the wave and also on the subatance (e.g its surface). For example, microwaves are reflected by metal surfaces but they can pass through paper.

Question 23

🟢 How Can You Test Sound Waves - How To Find Out The Speed of Sound Waves

Answer 23

Sound waves reflect from smooth hard surfaces, such as bare walls. If you clap your hands together in a large hall with bare walls, for example, a school gymnasium, you will hear the echo a short time later. The time delay is because the sound waves travel to the wall and back before you heart the echo.

If the distance ‘d’ to the nearest wall is measured and the time delay ‘t’ is also measured, the speed of sound un the air can be calculated using the equation:

Speed, s = Distance to the wall and back, ‘2d’ / Time Delay, ‘t’

Question 24

🟢 What Does The Ear Detect?

Answer 24

Your ear can detect an enormous range of sound waves of different intensities as well as a wide range of frequencies, from 20Hz to about 20kHz (20,000Hz). When sound waves make your ear drum vibrate, your ear sends signals to your brain about what you are hearing.

Question 25

🟢 How Does Sound Get Into The Ear, and How Does The Ear Interpret Sound Waves

Answer 25

• Sound waves entering a solid are converted to vibrations and travel through the solid as vibrations (sound travels through solids the fastest). The conversion of sound waves to vibrations of solids only works over a limited frequency range. So the frequency range of the human ear is limited.
• Sound waves travel through different substances at different speeds. When sound waves travel from one substance to another, their frequency does not change but their speed may change depending on the two substances, and so their wavelength may change. Therefore, the fequency of the sounds you listen to do not change when tne sound waves amd vibrations pass through the air and the different parts of their ear.

Question 26

🟢 What is Echo Sounding and What Can It Be Used For?

Answer 26

Echo sounding uses pulses of high-frequency sound waves to detect objects in deep water and to measure water depth below a ship, for example. An echo is the reflection of sound waves from a smooth surface. The pulses from the transmitter are reflected at the sea bed directly below the ship and detetcted by a reciever at the sa,e depth as the transmitter. The time taken, ‘t’, by each wave to travel to the sea bed and back is measured. The total distance travelled by the wave + vt, where v is the spped of sound in the water. This is twice the depth of the sea bed below the surface, so the depth of water below a ship is:

1/2 x vt

Question 27

🟢 What are Ultrasound Scanners Used For?

Answer 27

Ultrasound waves are used for prenatal scans of a baby in the womb. They are also used to get an image of organs in the body, such as a kidney, or damaged ligaments and msucles. An ultrasound scanmer is made up of an electronic device called a transducer placed on the body surface, a control system, and a display screen. The transducer produces and detects sets (or pluses) of ultrasound waves.

Question 28

🟢 What happens to Each Ultrasound Wave pulse from the Transducer

Answer 28

Each ultrasound wave pulse from the transducer:

• Is partially reflected from the different tissue boundaries in its path
• Returns to the transducer as a sequence of ultrasound waves refelcted by the tossue boundaries, arriving back at different times.

The transducer is moved across the surface of part of the body. The ultrasound waves are then detected by the transducer. They are used to build up an image on a screen of the internal tissue boundaries in the body.

Question 29

🟢 What are the Advantages of using Ultrasound over X-Rays

Answer 29

The advantages of using ultrasound waves for certain types of medical scanning are that ultrasound waves, unlike X-rays, are:

• Reflected at boundaries between different types of tissue (diffferent media), so they can be used to scan organs and other soft tissues in the body
• Non-ionising. Non-ipnising radiation is radiation that does not have enough energy to remove an electron to ionise an atom r molecule. So it is harmless when used for scanning.

Question 30

🟢 How Are Ultrasound Waves used in Industrial Imaging?

Answer 30

Ultrasound waves can be very useful in industrial imaging. Flaws in metals castings can be detected using ultrasound waves. A flaw might be an internal crack, which creates a boundary inside the metal. The ultrasound waves are partly reflected from this boundary. A transducer at the surface of the block sends ultrasound waves into the block. The reflected waves are detected by the transducer and displayed in an oscilloscope screen or a computer monitor.

Question 31

🟢 What would an Oscilliscope Show if there were cracks in metal, for example

Answer 31

The oscilliscope will show:

• A strong wave pulse due to partial reflection of the transmitted pulse at the surface, then
• Some further ultrasound wave pulses - in this case two due to partial reflection at internal boundaries, and the last wave pulse due to partial reflection at the far side of the metal object.

Question 32

🟢 Why Is It Useful That Ultrasound Waves are partially reflected by Organ Tissues (and why is’s bad if it passes through like in an X-Ray)

Answer 32

The partial reflection of the waves at different tissue boundaries allows an image to be formed with the results.

As X-Rays will pass through the organs unaffected, it will not be possibke to form an image.

Question 33

🟢 What does ‘Ionising’ mean

Answer 33

Ionising means there is enough energy to remove an electron from an atom, forming an ion - this can be harmful, as it can cause mutations in your DNA, which can possibly lead to cancer.

Question 34

🟢 Equation for Distance Travelled by a Wave

Answer 34

Distance Travelled By The Wave, m (meters) = Speed of Ultrasound Waves in body tissue, m/s X Time Taken (s)

Question 35

🟢 Equation for Depth of the Boundary Below The Surface when using ultrasound waves

Answer 35

The Depth of the Boundary Below the surface (m) = 1/2 x Speed of the Ultrasound Waves (m/s) X Time Taken (s)

Question 36

🟢 How Does The Distance of Boundaries from the Transmitter show the Time and Distance Travelled when using the Oscilloscope (+ Example of how this is useful in Medicine)

Answer 36

The further away a boundary is from the transmitter, the longer a reflected wave takes to return. You can use the oscilloscope to measure the time atken by the wave to travel from the transmitter at the surface to and from the boundary that reflected it.

Because the ultrasound waves travel from the surface to the boundary then back to the surface, the depths of the boundary below the surface is half the distance travelled by each wave to and from the boundary.

This principle is useful in medicine. Ultrasound waves are used by eye surgeons when they need to know how long an eyeball is.

Question 37

🟢 What Are Optical Fibres and How Are They Used

Answer 37

An optical fibre is a thin rod of high-quality glass. Very little light is absorbed by the glass. Light getting in at one end undergoes repeated total internal reflection, even when the fibre is bent, and emerges at the other end.

Optical Fibres:

• Are used in endoscopes that allow surgeons to see inside their patients.
• Can also carry enormous amounts of information as pulses of light.

Question 38

🟢 What Are Endoscopes and How Are They Used

Answer 38

Endoscopes use optical fibres to produce an image of inside the body. A doctor can insert a bundle of optical fibres into the body. Some carry light into the body, and some carry light reflected off internal body surfaces back out. This allows the doctor to see an image of the inside of the body clearly, and help them diagnose diseases like cancer, or see what they are doing during keyhole surgery.

Question 39

🟢 What Is Snell’s Law

Answer 39

Snell’s Law, also known as the Law of Refraction is used to describe the relationship between the angles of incidence and refraction, when reffering to light or other waves that pass through a boundary between two different mediums like air, and glass.

Question 40

🟢 What are the Top two layers of the Earth and how do they differ between the land and ocean (+Where are Earthquakes Generated)

Answer 40

Earthquakes are generated in the Earth’s crust. This is a solid layer of rock about 50km thick that surrounds a much thicker layer of molten rock called the mantle. The Earth’s crust beneath the oceans is much thinner and younger than the crust below the continents. The Earth has a solid inner core and liquid outer core beneath the mantle.

Question 41

🟢 How are Earthquakes recorded (+What is the focus and the epicentre)

Answer 41

Earthquakes happen inside the Earth’s crust. The point where an earthquake originates from is called it’s docus. The nearest point on the surface to the focus is called the epicentre of the earthquake. Earthquakes are recorded by detectors on the surfacw of the Earth called seismometers.

Question 42

🟢 What are the main three types of seismic waves

Answer 42

• Primary Waves (P-waves)
• Secondary Waves (S-waves)
• L-waves

Question 43

🟢 What are Primary Waves (P-Waves)

Answer 43

Primary Waves (P-waves) cause the initial tremors lasting about one minute. These are longitudinal waves that push or pull on material as they move through the Earth.

Question 44

🟢 What are Secondary Waves (S-Waves)

Answer 44

Secondary Waves (S-waves) cause more tremors a few minutes later. They are transverse waves that travel more slowly than P-waves. They shake the material that they pass through inside the Earth from side to side

Question 45

🟢 What are L Waves (don’t need to fully know)

Answer 45

L-waves arrive last and cause violent movements on the surface up and down as well as backwards and forwards. They travel more slowly than P-waves or S-waves, amd they only happen in the Earth’s crust.

Question 46

🟢 How do the different waves from a wave travel through the different layers of the Earth

Answer 46

When an earthquake happens, seismometer readings from different parts of the world are used to find out where its epicentre is.

• P-waves and S-waves bend as they travel through the mantle. This is because their speed changes gradually with depth, and so their direction changes with depth.
• P-waves refract at the boundary between the mantle and the outer core. This is because their speed changes abruptly at the boundary.
• S-Waves are transverse waves, and so they can’t travel through the liquid outer core

Question 47

🟢 What is the Shadow Zone and What 3 things does it show

Answer 47

When an earthquake happens, some seismometers record only long waves. These seismometers are in the shadow zone of the earthquake, which is a zone from about 105° to 142° where no P-waves or S-waves are recorded.

1. The existence of the shadow zone shows that there is a liquid (outer) core under the mantle because:
   - P-waves are refracted at the boundary between the mantle and the
   outer core when the waves enter the core and when they leave the
   core. Because the second refraction is further around, the waves
   can’t reach the shadow zone
   - S-waves can’t travel through the outer core, because they are
   transverse waves and can’t travel through liquid.
2. Weak P-waves detected in the shadow sone show that the core has a solid inner part that refracts P-waves at the boundary between the outer cire and the inner core into the shadow zone
3. The boundary between the crust and the mantle of the Earth was discovered when it was found that the speed of seismic waves changed at a depth of about 50km below the surface.

Question 48

🟢 What is the Shadow Zone

Answer 48

The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Question 49

🟢 What is the Amplitude of a Wave?

Answer 49

The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed position. It’s the height of the wave crest/trough from the middle.

The bigger the amplitude of the the waves, the more energy the waves carry.

Question 50

🟢 What two types of waves are there?

Answer 50

There are different types of waves. These include:

• Mechanical Waves, which are vibrations that travel through a medium (a substance). Sound waves, water waves, waves on springs and ropes, and seismic waves produced by earthquakes are all examples of mechanical waves.
• Electromagnetic waves are able to travel through a vacuum at the same speed of 300,000 kilometers per second. No medium is needed for them to travel. Examples imclude light waves, radio waves, and microwaves

Question 51

🟢 What is Compression and Rarefraction

Answer 51

Areas of compression are areas where the waves are more densly packed together, and rarefraction is the waves are further apart.

Question 52

🟢 What is Echo Sounding?

Answer 52

This technique is used to measure how deep the ocean is. This is important so ships do not head into shallow waters.

The ship transmits a high frequency sound wave. This is then reflected from the bottom of the ocean and is detected by the ship.
Rearrange the formula s=d/t, s=d/t d=s×t. This distance is twice the distance of the ocean so we divide it by two.
d=(s×t)/2

The speed of sound in water is 1,500 m/s, and knowing the time it takes to transmit and receive the sound we can calculate the distance.

Question 53

🟢 Example Question:

Calculate the depth of the ocean if a high frequency sound wave travelling at 1,500 m/s is transmitted and is received 5 seconds later.

Answer 53

1,500m/s x 5 = 7,500m

7,500m / 2 = 3750m

3750m

Question 54

🟢 What does Loud Noises, Quiet Noises, High Pitches, and Low Pitches look like on Oscilloscope Traces

Answer 54

Loud noise results in waves with large amplitude

Quiet noise results in waves with low amplitude

High pitches result in smaller wavelengths

Low pitches result in larger wavelengths

Question 55

🟢 Describe how sound waves are produced by a drum and then heard?

Answer 55

Sound waves are produced from the drum when the drum is hit and then vibrates. These vibrations cause sound waves. Sound waves are mechanical so they need matter to transfer energy of information through, making it a longitudinal wave. The sound waves pass through the matter of air and are directed into the ear canal through the outer ear (pinna) and the sound waves travel through to tbe tympanic membrane (eardrum). The ear drum vibrates, amplifying the sound to three small bones in the ear which then pass on these vibrations to the cochlea where they are then transferred to the brain and electronic nerve signals.

Question 56

🟢 Explain how a vibration becomes a sound that is heard?

Answer 56

Sound waves are produced from vibrations, as sound that we percieve is essentially multiple different vibrations at frequencies between 20Hz-20kHz. . Sound waves are mechanical so they need matter to transfer energy of information through, making it a longitudinal wave. The outer ear, (pinna), funnels the sound into the ear canal. Sound waves travel along the ear canal and cause the eardrum to vibrate. Three small bones transmit these vibrations to the cochlea. This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.

Question 57

🟢 Explain why the human ear hears sounds over a limited range of frequencies?

Answer 57

.The cochlea is only stimulated by a limited range of frequencies. This means that humans can only hear certain frequencies. The range of normal human hearing is 20 Hertz (Hz) to 20,000 Hz (20 kHz). The hairs in the human cochlea have different lengths and vibrate at different frequencies of sound. This is how the human ear puts together an electrical signal that contains all the different frequencies in the sound wave being received. The range of frequencies that a person can hear depends on the range of lengths of hairs in the cochlea. As a person ages, the shorter hairs that respond to higher frequencies stop working - this means that people tend to lose the ability to hear higher frequencies of sound as they grow older.

Question 58

🟢 What are Ultrasound Waves

Answer 58

Ultrasound waves are longitudinal vibrations that have a frequency higher than the upper limit of human hearing (above 20kHz)

Question 59

🟢 What is an Ultrasound Scanner?

Answer 59

An ultrasound scanner is an electronic device which makes use of a ‘transducer’ which can be placed on a surface through which it can send pulses of ultrasound waves which can then also be detected – the results can then be shown on a display screen.

Question 60

🟢 What are the uses of ultrasound scanners?

Answer 60

They can be:

Medical Imaging:

• Organs inside the body
• Look at damaged ligaments
• Look at damaged muscles
• Look at babies in the womb
• It can be used for pre-natal scans
• Ultrasound scanners can also be used for industrial purposes, such as inspecting materials for defects and damage

Question 61

🟢 How do Ultrasound Scanners Work

Answer 61

An ultrasound wave pulse from the transducer:

• Is partially reflected by different medium boundaries.
• Reflected waves return to the transducer with the time taken being monitored.
• As the reflected ultrasound waves are detected an image can be produced with the results for that point.
• The transducer is then moved around the object to get a full image.

Question 62

🟢 What do you think is meant by ‘echo-location’?

Answer 62

Echo-Location can be broken up in the words echo and location:

Echo - A repeated sound that is caused by the reflection of sound waves from a surface

Location - A particular place or position

Question 63

🟠 Equation for Finding Distance with Sound

Answer 63

Distance object/boundary is away (meters, m) = 1/2 Speed of Ultrasound wave (meters per second, m/s) x Time taken (seconds, s)

Question 64

🟢 Baby scans allow doctors to check the development of a baby in the womb, why can’t x-rays be used?d?

Answer 64

X-Rays can’t be used as they are ionising, so they can cause defects, which is especially dangerous for developing babies.

X-Rays also pass through organ tissues as organs don’t reflect the radiation. Ultrasound can show soft tissues inside of the body, but it dies show tissues as the organ tissue does reflect the waves back.

Question 65

🟢 What happens in an Earthquake/For an Earthquake to happen?

Answer 65

• Forces inside the Earth can build up and causing layers of rocks to move and break/fracture.
• The sudden fracture of the rocks releases large amounts of energy, causing a shock wave – which is called a seismic wave.
• Seismic waves can travel through the Earth and across its surface.
• The study of earthquakes is called seismology.

Question 66

🟢 What are S-Waves + Their Characteristics

Answer 66

• The S stands for secondary.
• They are Side to Side waves (transverse).
• They can only travel through solids.
• They are slower than P-waves.
• They are bent by the changing density of the rock.
• They are bent sharply when the material changes suddenly.

Question 67

🟢 What are P-Waves + Their Characteristics

Answer 67

• The P stands for primary. These are Push-Pull waves (longitudinal)
• They can travel through liquid and solid so they can travel through the
  earth’s core.
• They travel fast.
• They are bent by the changing density of the rock.
• They are bent sharply when the material changes suddenly.

Question 68

🟠 What are L-Waves + Their Characteristics

Answer 68

• L-waves (Long waves), arrive last and cause violent movements on the surface up and down as well as backwards and forwards. They travel more slowly than P-waves or S-waves, and they only happen in the Earth’s crust.

Question 69

🟢 Why don’t S-waves travel through the outer core?

Answer 69

Secondary waves are transverse and transverse can’t go through the earth core, as they can’t travel through any liquids

Question 70

🟢 Compare and contrast how the different waves move through the Earth

Answer 70

• P-Waves and S-Waves bend as they travel through the mantle . Their speed and direction change with depth
• P-Waves refract at the boundary between the mantle and the outer core (solid to liquid)
• S-Waves do not travel through the outer core
• L-Waves travel more slowly than P-wave or S-Waves, and they only happen in the Earth’s crust.

Question 70

🟢 Use the detection of different types of seismic waves to provide evidence for the presence of a liquid outer core in the Earth’s structure.
(6 marks)

Answer 70

Primary waves are waves which are transverse and travel the fastest. These waves can travel through the mantle and outer core as transverse waves can travel through both liquids and solids. Secondary waves are slightly slower travelling than primary waves, and can only travel through the mantle, as the waves are longitudinal and cannot travel through liquid. L-waves are the last type of waves to occur and are the most violent movements on the surface up and down as well as backwards and forwards. To find the prescence of the liquid outer core, primary will need to travel through there in order to be detected under/between the two shadow zones. You can detect waves by using a device called a seismometer (you know they are primary waves as no secondary or long waves can travel that far, or even through any outer core).