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:

1. Frequency
2. Period
3. Wavelength
4. Amplitude

Answer 3

1. The amount of waves passing in a second (measured in Hertz Hz. Determines pitch or colour)
2. The time it takes one wave to pass a point
3. The length in m from one point to the next identical point of a wave
4. 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 deeper 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 energy 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. [6 marks]

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, thickest part (the base) detecting hgih frequencies (up to 20000Hz) and the low, thinnest 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 through 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

Question 28

SP4g - Why does the P wave shadow zone exist?

Answer 28

• P Waves travel at a slower speed in liquid, so will refract (change direction), which creates the shadow zone.