SP4 Waves Flashcards
Transverse waves
particles oscillate perpendicular to the direction of wave travel
Longitudinal waves
particles oscillate parallel to the direction of wave travel
Amplitude
the distance between rest and highest point on a wave
Wavelength
distance between a point on a wave and the same point on the next wave
Frequency
number of waves passing a point per second, measured in Hz Hertz. = 1/time period
Time period
time it takes for a full cycle of the wave to pass a point. = 1/frequency
Compression
squashed up particles (lots), high pressure
Rarefaction
stretched out particles (fewer), low pressure
Velocity
speed of the wave in the direction its travelling
Wave speed (m/s) =
v =
distance (m) / time (s)
x / t
Wave speed (m/s) =
v =
frequency (Hz) x wavelength (m)
f x λ
Options for waves at boundaries
refraction
reflection
absorption
transmission
Refraction
the change in direction of a wave when it moves into a different medium
happens at the interface (boundary)
Light from medium with low density to high density
slows down, bends towards normal
Light from medium with high density to low density
speeds up, bends away from normal
Light travelling along the normal
doesn’t change direction between mediums
Change in direction in refraction happens because of
change in speed
Reflection
the wave bounces off the surface
Absorption
the wave disappears as the energy it’s carrying is absorbed by the material
Transmission
the wave passes through the material and is not absorbed or reflected
As speed changes
the wavelength changes
the frequency stays the sane
Path of sound through the ear
- sound waves enter the ear canal
- the eardrum is a thin membrane. sound waves make it vibrate
- vibrations are passed on to tiny bones which amplify the vibrations
- vibrations are passed on to the cochlea
- tiny hairs inside the cochlea detect these vibrations and create electrical signals called impulses
- impulses travel along neurones in the auditory nerve to reach the brain
Cochlea and its structure
can detect the different frequencies of sound reaching the ear.
tube shape, made up of fluid and membrane.
membrane is thick at the base, which detects high frequencies, and thin at the apex, which detected low frequencies.
the part of the membrane that vibrates depends on the frequency of the sound waves in the fluid.
hair cells along membrane detect vibrations - each is connected to a neurone that sends impulse to brain
Ultrasound
frequencies higher than 20,000 Hz
Animal use of ultrasound
use ultrasound waves to listen for echoes that come from the wave reflecting off things around them
Human use of ultrasound: sonar
equipment carried on ships/submarines to detect fish and find the depth of the sea (d = s x t)
ultrasound pulses are emitted and reflected by the sea bed
Human use of ultrasound: foetal scans
ultrasound scans can be used to make detailed images of unborn babies, to help doctors monitor their health
the probe emits and receives ultrasound waves. a gel is used to stop the ultrasound just reflecting from the skin. the ultrasound machine detects the time between sending the pulse out and receiving the echo. the displays show where the echoes came from. the further down the screen, the longer the echo took to return
Infrasound
frequencies less than 20Hz
Vibrations caused by earthquakes
Seismic waves
can travel though earth as
longitudinal P waves
transverse S waves
P waves
longitudinal
can travel trhough liquids and solids
S waves
transverse
can’t travel trhough liquid
Structure of earth’s core
crust
mantle
liquid outer core
solid inner core
Shadow zone
where S waves can’t be detected
P waves have one too, created by liquid outer core. some weak P waves can be detected in SZ shows that some of the waves must be reflecting off solid inner core
