SP4a - Describe a transverse wave, giving examples.
- Paritcles 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
SP4a - Describe a longitudinal wave, giving examples.
- Particles vibrate parallel to direction of travel
- Areas of compression and rarefraction
- Sound waves
- Seismic P waves
SP4a - Descirbe the following features of a transverse wave:
- 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
SP4b - What are the two formulas for wave speed?
v = d/t
(Velocity = distance ÷ time)
v = f x λ
(Velocity = frequncy x wavelength)
SP4b - Using two buoys, how can you measure the speed of waves?
- 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.
SP4b CP - How can you use a wave tank to investigate the speed of waves?
- 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
SP4b CP - How can you use a metal rod to investigate the speed of waves in solids?
- 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
SP4c - How does refraction occur?
- 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
SP4c - Using water waves as a model, explain why refraction occurs.
- 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
SP4d - What are the definitions of the following:
- 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
SP4d - Why is a prism able to split white light into a spectrum?
Each frequency of light changes speed at a slightly different rate meaning that at the right angles they can be split up
SP4e - Describe the process of a sound being heard by and ear. [6 marks]
- 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
SP4e - How does the cochlea work?
- 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)
SP4e - Explain why as people get older, their range of hearing may decrease.
- 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
SP4f - What is the human range of hearing?
20Hz - 20,000 Hz
SP4f - What is ultrasound?
Sound above 20,000 Hz
SP4f - How can boats use ultrasound in sonar equipment?
- 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
SP4f - How is ultrasound used in scans?
- 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
SP4f - Why is an ultrasound scan more beneficial for scanning a foetus?
- Other scans such as PET and CT would release radiation
- This could harm the foetus causing mutations
SP4g - What is infrasound?
Sound below 20Hz
SP4g - What are the two types of seismic waves and what is the difference?
- P waves: Longitudinal
- S waves: Transverse
SP4g - What are seismic waves?
Vibrations produces by earthquakes
SP4g - Why are P waves more useful than S waves?
- 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
SP4g - What is a shadow zone?
The area where a wave cannot reach when fired from a point
SP4g - What is the key thing to remember about seismic waves as they pass through the earth?
They get refracted
SP4g - Why may there still be weak P waves even in the shadow zones?
They can be reflected by the solid inner core
SP4g - How can seismic waves be used to detect earthquakes?
Seismic waves can be detected by seismometers and give information about where earthquakes are originating