waves Flashcards
what do waves transfer
energy and information in the direction they are travelling
what happens when waves go through a medium (object/substance)
the particles of the medium vibrate and transfer energy and information between each other, overall the particles stay in the same place
what is the amplitude of the wave
the displacement from the rest position to the crest or trough
wavelength
the length of the full cycle of the wave
frequency
the number of complete cycles of the wave passing a certain point per second
frequency unit
hertz (Hz)
what is the period of the wave
number of seconds it takes for one full cycle
period equ
1 / frequency
what wave has a perpendicular vibration to the direction of the wave travelling
transverse
examples of transverse waves
Most waves
all electromagnetic waves
S - waves
ripples and waves in water
what wave is parallel to the direction the wave travels
longitudinal
examples of longitudinal waves
sound waves
P - waves
what do longitudinal waves do to particles
squash up and stretch out the arrangement of the particles in the medium they pass though
wave speed equ
distance / time
v = x / t
OR
V = frequency x wavelength (upsidedown y)
V = f x y
experiment to measure the speed of sound (oscilloscope)
1) Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
2) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned wavelength on the display, but have moved exactly one wavelength apart.
3) Measure the distance between the microphones to find one wavelength
4) You can then use the formula to find the speed (v) of the sound waves passing through the air - the frequency (f) is whatever you set the signal generator to in the first place.
how to measure the speed of water ripples using strobe lights
1) Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.
2) Dim the lights and turn on the strobe light - you’ll see a wave pattern made by the shadows of the wave crests on the screen below the tank.
3) Alter the frequency of the strobe light until the wave pattern on the screen appears to ‘freeze’ and stop moving. This happens when the frequency of the waves and the strobe light are equal - the waves appear not to move because they are being lit at the same point in their cycle each time.
4) The distance between each shadow line is equal to one wavelength. Measure the distance between lines that are 10 wavelengths apart, then find the average wavelength
how can you use peak frequency to find the speed of waves in solids
1) Measure and record the length of a metal rod, e.g. a brass rod.
2) Set up the apparatus shown in the diagram, making sure to secure the rod at its centre.
3) Tap the rod with the hammer. Write down the peak frequency displayed by the computer.
4) Repeat this three times to get an average peak frequency.
5) Calculate the speed
what do waves do at boundaries
get absorbed, transmitted, reflected
what happens when a wave is absorbed
the wave transfers energy to the materials energy stores, the energy is transferred to a thermal energy store, leads to heating
what happens when a wave is transmitted
the wave carries on travelling through a new material
what happens when a wave is reflected
the incoming ray is neither absorbed or transmitted, but instead repelled away from the second material
what is refraction
waves hit a boundary which at an angle, this change of speed causes a change in direction
if it travels at normal speed, the wave is not refracted
what’s another way to talk about refraction
optical density
how does sound travel
as a wave
what are sound waves caused by
vibrating objects
what type of waves are sound waves
longitudinal waves
what determines which frequencies it can transmit
size
shape
structure
how do you hear sound
vibrations are passed to tiny bones in your ear
the cochlea turns the vibrations into electrical signals which get sent to your brain
the brain interprets the sound so you can hear them
the structure of all the parts vibrate to transmit the sound wave
what is ultrasound
sound with frequencies higher than 20,000 Hz
what happens to ultrasound waves at boundaries
get partially reflected
how can ultrasound be useful
medical imaging (pre natal exams)
industrial imaging (finding flaws in materials)
how does ultrasound help with medical imaging
ultrasound can pass through the body, they meet the boundary and is then reflected back and detected
it’s also completely dade
how does ultrasound work with industrial imaging
ultrasound enters the material and will usually be reflected by the far side, if there is a crack the waves will be reflected sooner
what is infrasound
sound waves with frequencies lower than 20 Hz so we can’t hear them
what are some examples of infrasound
animal communications
earthquakes, volcanoes, avalanche
what cause seismic waves
earthquakes and explosions
what can travel through earths core
P - waves
what can’t travel through earths core
S - waves
p wave facts
longitudinal
travel through solids and liquids
faster than S - waves
S - waves facts
transverse
only travel through solids
slower than P - waves
