waves - topic 3 Flashcards
what is a wave
an oscillation that transfers energy and information without transferring any matter
what is an oscillation
a vibration
name the 2 types of waves
transverse
longitudinal
what are transverse waves
waves which oscillate at right angles to the direction they travel in and transfer energy and information in
name 3 examples of transverse waves
light and the other EM waves
ripples on water
waves on springs/ strings
what are longitudinal waves
oscillation that are parallel to the direction of travel of the wave and have areas of rarefaction and compression
name 3 types of longitudinal waves
sound waves
a spring when you push on the end
P waves
what do waves transfer
energy and information but NOT MATTER
examples of wave transfer
ripples on water surface cause floating objects to bob up and down. They don’t move the object across the water to the edge. This is proof the wave travels, not the water
what is a crest
highest point of a wave
what is trough
lowest point in a wave
what is amplitude
displacement from undisturbed position to a crest or trough
what is wavelength
distance between the same point on two adjacent waves
what is frequency
number of complete waves passing a certain point per second
what is the period of a wave
the amount of time it takes for a full cycle of the wave to be complete
equation for period of a wave
1/ frequency
what is a period measured in
seconds
what is frequency measured in
Hz
what is distance measured in
M
what is wave speed measured in
M/s
what is the equation for wavespeed
distance/ time
how to find distance between wave source and reflective surface
find total distance travelled by the wave and divide by 2
equation for wavelength
wavespeed/ frequency
how to measure speed of sound in the air
- set up equipment with both microphones next to the speaker
- slowly move one microphone away from the speaker
- keep it moving until 2 traces on the oscilloscope are aligned once more
- measure wavelength
- use formula wavespeed = frequency x wavelength to find speed
- speed of sound is 340m/s so check your results against this
how to measure speed of water ripples
- set up ripple tank with about 5 cm of water
- adjust height of wooden rod so that is just touches the surface of the water
- switch on the lamp and motor and adjust until low frequency waves can be clearly observed
- measure length of a number of waves then divide by number of waves to find wavelength
- count the number of waves passing a point in 10s then divide by 10 to find frequency
- calculate speed using v = f x y
how to measure waves in a solid
- using the first finger and thumb on the one hand, hold a metal rod at its middle point
- hit one end of the rod with a hammer
3, hold a smartphone with an app which measures frequency, near the end of the rod
- record the peak frequency
- measure and record the length of the metal rod
- calculate the speed of the waves using the frequency and wavelength
what 3 things can happen when a wave arrives at a boundary
absorption by 2nd material which transfers energy to material
reflection - waves may bounce back from 2nd material
transmission - waves may carry on travelling however they often undergo refraction
when does refraction occur
Refraction occurs when light changes direction as it passes from one medium to another due to the change in its speed.
what happens to the angle of refraction if a refracted ray bends towards the normal
angle of refraction will be smaller than angle of incidence
how to investigate refraction
place glass block one a piece of paper and trace around
use ray box to shine a ray of light at the middle of one side of the box
trace the incident ray on the paper and do the same for the light ray
remove the block and join up both rays to find the path of the refracted ray
draw the normal at the point where light entered the block
use a protractor to measure angle of incidence and refraction
repeat 3 times, keeping angle of incidence the same and calculate and average for each angle
what happens if a wave slows down at a boundary
it bends towards the normal
what happens if a wave speeds up at a boundary
it bends away from the normal
what are sound waves
sound waves are longitudinal waves of vibrating particles caused by vibrating objects
what happens to sound waves as they enter different materials
they will refract
what happens when a sound wave meets a solid object
air particles hitting the object causes the closest particles in the solid to vibrate and this continues. This series of vibrations passes sound waves through the object
how do we hear things
sound waves of certain frequencies that reach your ear drum cause it to vibrate
vibrations passed on to tiny bones in the ear through the semicircular canals and to the cochlea
the cochlea turns vibrations into electrical signals, sent to the brain
this allows you to hear sounds
what frequencies can humans hear between
20 Hz to 20,000 Hz
why is there a limit to the frequency we can hear between
due to the size and shape of our ear drums
what is ultrasound
sound wavs with frequencies greater than 20,000 Hz and so it can’t be heard by people
what can ultrasound be used for
foetal scanning, sonar ( which is used in the military or commercial fishing
how is ultrasound used in foetal scanning
to produce an image of an unborn baby so we can identify any problems with the baby’s development early
what is active sonar
a type of sonar used by boats and submarines where high frequency sound waves are used to find out the depth of water or to locate objects
how active sonar is used to find out the depth of objects or locate objects
a pulse of sound waves is emitted by submarine and the time taken for the echo to return is measured. Then if you know the speed of sound in water you can find depth using distance = wavespeed x time
infrasound
sound waves with frequency below 20 Hz
what is infrasound used for
detecting distant volcanic eruptions or in exploring structures and properties of the Earth’s core
how ultrasound waves are used to detect fishes
ultrasound waves go down through the water. ultrasound waves are reflected off fish. reflected ultrasound waves are received by boat. time delay shows how
deep fish are
what are wavefronts
imaginary lines drawn through identical points on waves
what is wave speed
how fast a wave moves, or how fast it transfers energy or information
what is wave velocity
the speed of a wave in a certain direction
what are the 2 types of seismic waves
p waves and s waves
what are p waves
longitudinal waves which can travel through both solids and liquids and travel faster in solids
what are s waves
transverse waves which can only pass through solids
how are seismic waves used to explore the earth’s structure and core
by measuring the seismic waves detected at various points on Earth , seismologists can build up a picture of the paths the waves have travelled along from the point of origin to points of detection . This allows them to work out any boundaries between different materials within Earth.
what do seisometers do
seismic waves from an earthquake can be detected at different points on the surface of the planet using seisometers
