SP4 - Waves

Question 1

SP4a - Describe a transverse wave, giving examples.

Answer 1

• Particles vibrate perpendicular to their direction of travel.
• They transfer energy
• They all travel at the same speed in a vacuum (3x108)
• All EM waves are examples of this
• Water waves are transverse

Question 2

SP4a - Describe a longitudinal wave, giving examples.

Answer 2

Particles vibrate parallel to direction of travel
Areas of compression and rarefraction
Sound waves
Seismic P waves

Question 3

SP4a - Descirbe the following features of a transverse wave:

Frequency
Period
Wavelength
Amplitude

Answer 3

• The amount of waves passing in a second (measured in Hertz Hz. Determines pitch or colour)
• The time it takes one wave to pass a point
• The length in m from one point to the next identical point of a wave
• The distance in m from a waves rest position to its trough or peak

Question 4

SP4b - What are the two formulas for wave speed?

Answer 4

v = d/t

(Velocity = distance ÷ time)

v = f x λ

(Velocity = frequncy x wavelength)

Question 5

SP4b - Using two buoys, how can you measure the speed of waves?

Answer 5

Measure the distance the buoys are apart.
Record the amount of time it takes for a single wave to get from one to the other.
Do distance/time to get the wave speed.

Question 6

SP4b CP - How can you use a wave tank to investigate the speed of waves?

Answer 6

Set up a wave tank filled with water and a straight dipper with a ruler along the side
Vary the voltage provided to the straight dipper till there are at least 2 waves visible at any point
Count how many waves form in 10 seconds and divide by 10 to get your frequency
Using the ruler estimate the wavelength of a wave
Frequency x wavelength
Alternatively, record how long it takes the wave formed to travel a certain distance and to distance/time

Question 7

SP4b CP - How can you use a metal rod to investigate the speed of waves in solids?

Answer 7

Suspend a metal rod using clamp stands
Hold a smartphone with a frequency app at one end
Hit the other end of the rod with a hammer and record the peak frequency
Meausure the length of the rod
Frequency x wavelength

Question 8

SP4c - How does refraction occur?

Answer 8

When a ray of light reaches an interface (boundary) between substances, it changes speed (because light’s speed is dependant on the density of the substance it travels in).
If it slows down it bends towards the normal and if it speeds up it bends away

Question 9

SP4c - Using water waves as a model, explain why refraction occurs.

Answer 9

Waves of water travel faster is depper water than shallow water
They also are longitudinal so can be represented with lots of parallel lines rather than one line
When the wave of water reaches a boundary between shallow and deep, the part of each line that is furthest ahead, will reach the boundary first and slow down first.
This gradual change in which parts slow down means that the wave bends towards the normal

Question 10

SP4d - What are the definitions of the following:

Reflect
Refract
Transmit
Absorb

Answer 10

Reflect: The waves bounce off
Refract: The wave passes into the new material but changes direction
Transmit: The wave passes through without being absorbed or reflected
Absorbed: The wave disappears as the enrgy it was carrying is transferred into the material

Question 11

SP4d - Why is a prism able to split white light into a spectrum?

Answer 11

Each frequency of light changes speed at a slightly different rate meaning that at the right angles they can be split up

Question 12

SP4e - Describe the process of a sound being heard by and ear.

Answer 12

Sound waves enter the ar canal which focuses it
The eardum is a thin membrance which vibrates due to the soundwaves’ vibrations
Vibrations are passed on to tiny bones which amplify the vibrations
Vibrations are passed on to the liquid inside the cochlea
Tiny hairs inside the cochlea detect these vibrations and convert them to electrical impulses
Impulses travel along the auditory nerve to reach the brain

Question 13

SP4e - How does the cochlea work?

Answer 13

The cochlea has a membrane covered with hair cells
Each hair cell is connected to a neurone so that when it detects a vibration of its frequency it creates and electrical signal
The cochlea is a spiral with the outmost part (the base) detecting hgih frequencies (up to 20000Hz) and the low end (the apex) detecting lower frequencies (down to 20Hz)

Question 14

SP4e - Explain why as people get older, their range of hearing may decrease.

Answer 14

As people get older, the hairs of the base and apex of their cochlea can get damaged.
This means that they are no longer able to convert vibrations into impulses
Thus they can’t hear these sounds

Question 15

SP4f - What is the human range of hearing?

Answer 15

20Hz - 20,000 Hz

Question 16

SP4f - What is ultrasound?

Answer 16

Sound above 20,000 Hz

Question 17

SP4f - How can boats use ultrasound in sonar equipment?

Answer 17

To find the depth of the water beneath them.
They fire off an ultrasound wave at 1500m/s.
They time how long it takes to return.
They use d = s x t to find out the distance hte wave travelled and divide it by 2 to find the depth of the water

Question 18

SP4f - How is ultrasound used in scans?

Answer 18

A probe emits ultrasound waves
Gel is used to stop it from reflecting
Some waves are reflected when they meet bones, fat, tissue etc.
The probe also detects these refelected waves
It sends these as impulses to the computer
The ultrasound imaging machine detcts the frequency of the impulses turning it into an image

Question 19

SP4f - Why is an ultrasound scan more beneficial for scanning a foetus?

Answer 19

Other scans such as PET and CT would release radiation
This could harm the foetus causing mutations

Question 20

SP4g - What is infrasound?

Answer 20

Sound below 20Hz

Question 21

SP4g - What are the two types of seismic waves and what is the difference?

Answer 21

P waves: Longitudinal
S waves: Transverse

Question 22

SP4g - What are seismic waves?

Answer 22

Vibrations produces by earthquakes

Question 23

SP4g - Why are P waves more useful than S waves?

Answer 23

P waves are longitudinal while S waves are transverse
S waves can only be transmitted by solids but P waves can go through all through states
The earth has a liquid outer core
S waves fired from a point can’t go throuhg the liquid core but P waves can
This means that S waves have a larger shadow zone
Using the idea that S waves can’t go through liquids and P waves can, scientists were able to find out about the structure of the earth

Question 24

SP4g - What is a shadow zone?

Answer 24

The area where a wave cannot reach when fired from a point

Question 25

SP4g - What is the key thing to remember about seismic waves as they pass through the earth?

Answer 25

They get refracted

Question 26

SP4g - Why may there still be weak P waves even in the shadow zones?

Answer 26

They can be reflected by the solid inner core

Question 27

SP4g - How can seismic waves be used to detect earthquakes?

Answer 27

Seismic waves can be detected by seismometers and give information about where earthquakes are originating