Topic 6 - waves Flashcards
(122 cards)
1
Q
what happens when a wave travels through a medium
A
when waves travel through a medium - the particles of the medium oscillate and transfer energy between each other. But overall , the particles stay in the same place - only energy is transfered
2
Q
what happens when you drop a twig in a calm pool of water
A
ripples form on the waters surface. the ripples dont carry the water away with them though
3
Q
what happens when you strum a guitar string
A
create sound waves
they dont carry air away from the guitar
4
Q
what is the amplitude of a wave
A
the maximum displacement of a point on the wave from its undisturbed position
5
Q
what is wavelength
A
the distance between the same point on two adjacent waves
e.g. crest to crest or trough to trough
6
Q
what is frequency and what is it measured in
A
number of complete waves passing a certain point per second
measured in hertz
7
Q
what is the period of a wave and what is the equation for finding it out
A
the amount of time it takes for a full cycle of the wave
T (period in seconds ) = 1/f (frequency hz)
8
Q
what is a tranverse wave and give examples
A
the oscillations are perpendiculare to the direction of energy transfer
electromagnetic waves e.g. light
ripples and waves in water
a wave on a string
9
Q
what is a longitudinal wave and give examples
A
the oscillations are parallel to the direction of energy transfer
sound waves in air , ultrasound
shockwaves e.g. some seismic waves
10
Q
what is the equation to calculate wave speed
A
wave speed m/s = frequency x wavelength (m)
11
Q
what is wave speed
A
the speed at which energy is being transferred
12
Q
what is the method for measuring the speed of sound
A
equipment
speaker
oscilloscope
2 microphones
- turn speaker to 50 hz
- both microhpones will detect sound waves at the same time
- begin moving one microphone away from the speaker
- the lines on the oscilloscope will not be syncronised
- stop when the lne have syncronised again
- excactly one wavelength apart
- measure distance between microphones
use soeed = frequency x wavelength
13
Q
describe the ripple tank required practical
A
equipment:
ripple tank (used to observe features of waterwaves )
contains a vibrating bar connected to power pack (creates waves)
record using mobile phone to play back at different speeds / observe more accurately
- place ruler on paper which is under the tank
- freeze the image of the waves
- measure the wavelengths of ten waves
- divide by ten to find one wavelength
to find frequency :
1. place timer next to paper and count number of waves passing a cretain point in one second
2. do it for ten seconds and divide by ten
using fequency and wavelength , use
speed = frequency x wavelength
14
Q
describe the practical for waves in a solid
A
equipment
string with one end attached to a vibration generator
attach a hanging mass to the other end
the mass keeps the string pulled tight
vibration generator attached to a signal generator which allows us to change the frequency og vibration of the string
- turn one the power so the string vibrates
- at a certain frequency you will be able to see a wave shape called a standing wave , this is due to resonnance
- use a ruler to meaure the wavelength of the standing wave from the generator to the wooden bridge
some frequencies produce half wavelengths
to calculate wavelength
divide total length by number of half wavelengths then multiply by 2
15
Q
what three things can happen when waves arrive at a boundry between two different materials
and what determines what happens
A
the waves are absorbed by the material the wave is trying to cross into - this transfers energy to the materials energy stores
the waves are transmitted - the waves carry on travelling through the new material - this leads to refraction
the waves are reflected
what happens depends on the wavelength and the properties of the materials involved
16
Q
what is the one main simple rule for all reflected waves
A
angle of incidence = angle of reflection
17
Q
what is the angle of incidence
A
the angle between the incoming wave and the normal
18
Q
what is the angle of reflection
A
the angle between the reflected wave and the normal
19
Q
what is the normal
A
an imaginary line that is perpendicular to the surface at the point of incidence
usually shown as a dotted line
20
Q
what is the point of incidence
A
the point where the wave hits the boundary
21
Q
what is specular reflection
A
happens when a wave is reflected in a single direction by a smooth surface .
e.g. when light is reflected by a mirror you get a nice clear reflection
22
Q
what is diffuse reflection
A
when a wave is reflected by a rough surface ( e.g. a piece of paper ) and the reflected rays are scattered in lots of different directions .
this happends because the normal is different for each incoming ray which means that the angle of incidence is different for each ray . the rule of angle of incidence = angle of reflection still applies .
when light is reflected by a rough surface , the surface apears matte and you dont get a clear reflection of objects
23
Q
describe the features of electromagnetic waves
A
all EM waves are transverse waves that transfer energy from a source to an absorber
all EM waves travel at the same speed through air or a vacuum
they form a continuous spectrum over a range of frequencies
24
Q
what are the seven basic types of electromagnetic waves and describe the patterns in the way they are ordered
A
1.radio waves long wavelength low frequency
2.micro waves
3.infra red
4.visible light
5.ultra violet
6.x-rays
7.gamma rays short wavelength high frequency
25
why is there such a large range of frequencies in EM waves
they are generated bu a variety of changes in atoms and their nuclei e.g. changes in the nucleus of an atom creates gamma rays .
this also explains why atoms can absorb a range of frequencies - each one causes a different change
26
what is refraction
when a wave crosses a boundry between materials at an angle and it changes direction
27
what does how much a wave is refracted depend on
how much the wave speeds up or slows down .
which usually depends on the density of the two materials (higher density of material , slower the wave will travel through it )
28
what happens if a wave crosses into a material and speeds up /slows down
if it speeds up , it will bend away from the normal
if it slows down it will bend towards the normal
29
what in a wave changes and stays the same during refraction
the wavelength of a wave changes but the frequency will stay the same
30
what happens to a wave if it is traveling along the normal into another material
it will change speed but is not refracted
31
what is the optical density of a material
a measure of how quickly light can travel through it .
the higher the optical density, the slower light waves travel through it .
32
how can you construct a ray diagram for a refracted light ray
1. draw the boundry between two materials and the normal
2. draw an incident ray that meets the normal at the boundry
the angle between the ray and normal is the angle of incidence
3. draw the refracted ray on the other side of the boundey
if the second material is optically denser than the first, the refracted ray bends towards the normal .
the angle between the refracted ray and normal is smaller than the angle of incidence . if the second material is less o;tically dense, the angle of refraction is larger than the angle of incidence
33
describe the practical for investigating refraction with transparent materials .
1. place a transparent block on a piece of paper and trace around it. use a ray box or laser to shine a ray of light at the middle of one side of the block .
2. trace the incident ray and mark where the light ray emerges on the other side of the block . remove the block and with a straight line , join up the incident ray and the merging point to show the path of the refracted ray through the block .
3. draw the normal at the point where the light ray entered the block . use a portractor to measure the angle between the incident ray and the normal and the angle between the refracted ray and the normal .
4. repet using rectangular blocks made from different materials keepinf the incidence angle the same throughout.
control variable - do in dark room, use ray box or laser to produce thin rays of light so you can easily see the middle of the ray when tracing it and measuring angles from it.
34
how can you investigate how much different materials reflect light and describe the results
1. draw a straight line across a piece of paper and place an ovject so that one of its sides lines up with the line .
2. shine a ray of light at the objects surface and trace the incoming and reflected light beams .
3. draw the normal at the point where the ray hits the object. use a portracter to measure the angle of incidence and reflection and record these values .also makenot of the width andbrightnessof thereflected light ray .
4. repeat for a range of objects
you should see that smooth surfacs like mirrors give clear reflections ( the reflected ray is as thin and bright as the incident ray )
rough surfaces like paper cause diffuse reflection which causes the reflected beam to be wider and dimmer
the angle of incidenc is always equal to the angle of relection
35
what are Electromagnetic waves made of
oscillating electric and magnetic fields .
36
describe how radio waves can be produced
using an alternating current in an electrical circuit. the object in whihch charges oscillate to create the waves is called a transmitter .
when transmited radio waves reach a reciever, the waves are absorbed.
the energy carried by the waves is transferred to the electrons in the material of the reciever.
this energy causes the electrons to oscilate and if the reciever is part of a complete electrical circuit, it generates an alternating current .
this current has the same frequency as the radio wave that generated it.
37
how long is a radiowave wavelength
over 10 cm
38
why can long radiowaves be transmitted across the world
long wavelengths diffract (bend( around the curved surfaces of the earth .
they can also diffract around hills, into tunnels and more.
therefore radiowaves can be recieved even if the reciever isnt in line of sight of the transmitter.
39
how long is a long radio wave
1-10 km
40
how long is a short radio wave
10m -100m
41
what is the ionosphere
an electrically charged layer in the earths upper atmosphere
42
can short radio wave signals be recieve at long distances from the transmitter
why
yes
they are reflected from the ionosphere
43
give an example of a short wave radio wave
bluetooth
44
can medium wave signals be reflected from the ionosphere
ometimes
it depends on atmospheric conditions and time of day
45
describe the radiowaves used for tv and fm radio transmissions
very short wavelengths
to get reception you must be in direct sight of the transmitter - the signal doesnt bend or travel far through buildings
46
how do satelites in the earths atmosphere use microwaves and why
communication to and from satellites uses microwaves
its best to use microwaves which can pass easily through the earths watery atmosphere .
for satelite tv , the sinal from a transmitter is transmitted into space,
where it is picked up by the satelite reciever dish orbitive above the earth ,
the satelite transmits the signal back to earth in a different direction ,
where its recieved by a satelite dish on the ground .
47
how do microwave ovens use microwaves
in microwave ovens, the microwaves are absorbed by water molecules in food
the microwavespenetrate up to a few centimetres into the food before being absorbed and transfereing the energy they are carrying to the water molecules in the food, causing the water to heat up .
the water molecules then tranfer this energy to the rest of the molecules in the food by heating - which quickly cooks foo,d
48
where does infrared radiation come from
given out by hot objects.
the hotter the object, the more IR radiation is given out
49
what can be used to detect infrared radiation and how does it work
infrared cameras
the camera detects IR radiation and turns it into an electrical signal , which is displayed on a screen as a picture. the hotter the object, the brighter it appears.
50
what can infrared radiation be used for
food can be cooked using IR radiation - the temperature of food increases when it absorbs IR radiation
electric heaters contain a long piece of wire that heats up when a current flows through it . this wire wire then emits lots of infrared radiation .
this emitted ir radiation is absorbed by objects and the air in the room - energy is transferred by the IR waves to the thermal energy stores of the objects, causing their temperatures to increase
51
what are fibre optic cables , what EM wave does it use , how and why
thin glass or plastic fibres that can carry data over long distances as pulses of visible light .
they work because of reflection , the light rays are bounced back and forth untill they reach the end of the fibre
visible light is used
light is not easily absorbed or scattered as it travels along a fibre
52
what is fluorescence
a property of certain chemicals, where ultra violet radiation is absorbed and then visible light is emitted.
53
how do fluorescent light works and why are they good
generate uv radiation which is absorbed and re emitted as visible light by a layer of a compound called a phosphor on the inside of the bulb
they are energy efficient so they are good to use when light is needed for long periods
54
what are security pens used for
can be used to mark property with your name .
under uv light the ink will glow , but its invisible otherwise .
this can help the police identify your property if its stolen
55
where is UV radiation produced and what does exposure to it do
produced by the sun
exposure to it gives people a suntan
when its not sunny some people go to tanning salons where UV lamps are used to give them an artificial suntan . however, overexpoure to uv radiation can be dangerouds
56
what can x rays pass through
easily through flesh but not easily through denser materials like bone or metal
57
what is a negative x ray image
the bright areas on the image are where few x rays get through
the plate starts of white
the more x rays that go through the darker it is
58
what can radiographers use to treat people with cancer and why
x rays and gamma rays
high doses of these rays kill all living cells so they are carefully directed towards cancer cells , to avoid killing too many normal healthy cells
59
what is a medical tracerr
where a gamma emmiting source is injected into the patient and its progress is followed around the body
gamma radiation i s well suited to this because it can pass through the body to be detected
60
what can radiographers do to protect theirselves from x rays and gamma rays
wear lead aprons and stand behind a lead screen or leave the room to keep their exposure to them to a minimum
61
what can radiographers do to protect theirselves from x rays and gamma rays
wear lead aprons and stand behind a lead screen or leave the room to keep their exposure to them to a minimum
62
what are the effects of each type of radiation based on
how much energy the wave transfers
low frequency waves like radiowaves dont transfer much energy and so mostly pass through soft tissue without being absorbed
high frequency waves like uv , x rays and gamma rays all transfer lots of energy and so can cause a lot of damage
63
what damage does uv radiation cause
damages surface cells which can lead to sunburn and cause skin to age prematurely
some serious effects are blindness and increased risk of skin cancer
64
what damage can x rays and gamma rays do
can cause gene mutation or cell destruction , and cancer
65
what is radiation dose and what is it measured in
what does it depend on
measured in sieverts Sv
a measure of the risk of harm from the body being exposed to radiation
total amount of radiation absorbed and how harmful the type of radiation is
66
how many millisieverts is in a sievert
1000
67
what is a ct scan and what are the radiation risks
uses x rays and a computer to build up an image of the inside of a patients body
radiation dose recieved in different parts of the body cause different amounts of damage
68
describe a convex lens
bulges outwards
auses rays of light parallel to the axis to be brought together(convulge) at the principal focus
69
describe a concave lens
caves inwards
it causes parallel rays of light to spread out (diverge)
70
what are each of these things
axis
principle focus of a convex lens
principle focus of a concave lens
focal length
a line passing through the middle of the lens - axis
where rays hitting the lens parallel to the axis meet
the point where rays hitting the lens parallel to the axis appear appear to all come from - you can trace them back untill they a ll appear to meet up at a point behind the lens
focal length - the distance from the centre of the lens to the principal focus
71
what are the three rules for refraction in a convex lens
an incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
an incident ray passing throuhg the principal focus regracts through the lens and travels parallel to the axis
an incident ray passing through the centre of hhe lens carries on in the same direction
72
what are the three rules for refraction in a concave lens
an incident ray parallel to the axis refracts through the lens and travels in line with the principal focus (so it appears to have come from the principal focus )
an incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis .
an incident ray passing through the centre of the lens carries on in the same direction
73
what is a real image
where the light from an object comes to form an image on a screen - like the image formed on an eyes retina
74
what is a virtual image
when the rays are diverging so the light from the object appears to be coming from a completely different place
when you look in the mirror you see a virtual image because the object(you) appears to be behind the mirror
you can get virtual image when looking at an object through a magnifying lens - the virtual image looks bigger than the object actually is
75
what 3 things do you need to say to describe an image properly
how big it is compared to the object
whether its upright or inverted relative to the object
whether its real or virtual
76
how would you draw a ray diagram for an image through a convex lens
pick a point on the top of the object .
draw a ray going from the object to the lens parallel to the axis of the lens .
draw another eay from the top of the object going through the middle of the lens .
the incident ray thats parallel to the axis is refracted through the principle focus on the other side of the lens
draw a refracted ray passing through the principle focus
the ray passing through the middle doesnt bed
mark where the rays meet. thats the top of the image
repeat the process for a point on the bottom of the object when the bottom of the object is on the axis ,the bottom of the image is also on the axis.
77
how would you draw a ray diagram for an image through a concave lens
pick a point on the top of the object .
draw a ray going from the object to the lens parallel to the axis of the lens .
draw another ray from the top of the object going through the middle of the lens
the incident ray thats parallel to the azis is refracted so it appears to have come from the principal focus. draw a ray from the principal foculs . make it dotted before it reaches the lens .
the ray passing through the middle of the lens doesnt bend
mark where the refracted rys meet . thats the top of the image
repeat for a point on the bottom of the object . when the bottom of the object is on the axis the bottom of the image is also on the axis .
78
what type of images do concave lenses always produce
virtual image
the image is the right way up , smaller than the object and on the same side of the lens as the object no matter where the object is .
79
how do magnification glasses work
create a magnified virtual image
the object being magnified must be closer to the lens than the focal length
since the image produced is a virtual image, the light rays dont come from the place where the image appears to be .
you cant project a virtual image onto a screedn
80
what is the formula for magnification
image height / object height
81
what are the range of light colours that we can see / the sizes
violet at 400 nm to reds ar 700 nm
82
what are the primary light colours
red ,green , blue
83
what are opaque objects
objects that do not transmit light
when visible light waves hit them , they absorb some wavelengths of light and reflect others
84
what does the colour of an opaque object depend on
which wavelengths of light are most strongly reflected
the other wavelengths of light are absorbed
85
what does the colour of an opaque object depend on
which wavelengths of light are most strongly reflected
the other wavelengths of light are absorbed
86
what wavelengths of light do white objects reflect
all of the wavelengths of visible light
87
what do black objects do with wavelengths
absorb all wavelengths of visible light
88
what are transparent and translucent objects
transparent - see through
translucent - artially see through
they transmit light , i.e. not all light that hits the surface of the object is absorbed or reflected - some can pass through
89
whata re colour filters used for
to filter out different wavelengths of light so that only certain colours are transmitted - the rest are absorbed
90
how do primary colour filters work
only transmits that colour . e.g. if white light is shone at a blue filter , only blue light willl be let through . the rest will be absorbed.
if you look at a blue object through a blue colour filter it will look blue because blue light is reflected from the objects surface and transmitted by the filter.
if the object was another colour, the object would appear black when viewed through a blue filter. all of the light reflected by the object will be absorbed by the filter.
91
what do filters that arent for primary colours do
let through both the wavelenths of light for that colour and the wavelenths of the primary colours that can be added otogether to make that colour
92
an object that is hotter than its surroundings will emit how much infrared radiation in comparission to what it absorbs when it cools down
more
93
describe the IR radiation emitted from objects at constant temperatures
emit it at the same rate as they are absorbing it.
94
give examples of how some colours and surfaces aborb and emit radiation better than others
black surfaces are better at absorbing and emitting radiation than a white one
matt surfaces are better at absorbing and emitting radiation than a shiny one
95
what is a leslie cube
a holow watertight metal cube made of e.g. aluminium whose four vertical faces have different surfaces .
you can use them to investigate IR emission by different surfaces
96
what is a leslie cube
a holow watertight metal cube made of e.g. aluminium whose four vertical faces have different surfaces .
you can use them to investigate IR emission by different surfaces
97
describe how you can investigate infrared emission using a leslie cube
1. place an empty leslue cube on a heat proof mat
2. boil water in a kettle and fill the leslie cube with water.
3. wait for a while for the cube to warm up then hold a thermometer against each of the four vertical faces of the cube. you should find that all our faces are the same temperature .
4. hold infrared detecter a set distance e.g. 10cm away from one of the cubes vertical faces and record the amount of IR radiation it emits.
5. repeat the measurement for each of the cubes vertical faces. makes sure you position the detecter the same distance from the cube each time.
6. more infrared radiation from the black surface and matt shout be detected.
7 repeat experiment and calculate the mean .
98
what is a perfect black body
an object that absorbs all of the radiation that hits it
99
what does the intenisty and distribution of the wavelength emitted by an object depend on t
the objects temperature
100
what is intensity
the power per unit area
how much energy is transferred to a given area in a certain amount of time
101
what increases as the temperature of an objectincreases
the intensity of every emitted wavelenght increases
102
does intensity increase more rapidly with longer or shoter wavelengths
short
this causes the peak wavelength to deacrese
103
what does the overall temperature of the earth depend on
the amount of radiation it reflects , absorbs and emits
104
what causes an increase in local temperature on earth
during the day lots of radiation is transfered from the sun and absorbed
105
what causes an increase in local temperature on earth
during the day lots of radiation is transfered from the sun and absorbed
106
what are sound waves caused by
vibrating objects
these vibrations are passed through the surrounding medium as a series of compressions and rarefactions
107
what state of matter do sound waves generally travel faster in
solids
108
why cant sound travel in space
it is a vacuum
no particles
109
why cant sound travel in space
it is a vacuum
no particles
110
what happens when sound waves enterour ears
reach our ear drum and cause it to vibrate
these vibrations are passed to tiny bones called ossicles through the semicircular canals and to the cochlea
the cochlea turns these vibrations into electrical signals which get sent to the brain .
111
what is the sound range in humans
20 hz - 20 khz
112
what is human hearing limited by
size and shape of ear drum
structue of parts within the ear that vibrate to transfer the energy from the sound waves
113
what are sound waves reflected by
hard surfaces
114
when do sound waves refract
when they enter a different medium
as they enter a denser medium , they speed up
this is because when a wave travels into a diff medium its wavelength changes but its frequesncy stays the same so its speed must also chagne
115
what is ultrasound
electrical devices can be made which produce electrical oscillations over a range of frequencies.
these can easily be converted into mechanical vibrations to produce sound waves beyonf the range of human hearing
116
how does ultrasound work
when a wave passes from one medium to another some of the wave is reflected off the boundry between the two mediums and some is transmitted
this is partial reflection
this means that you can point a pulse of ultrasound at an object and wherever there are boundaries between one substance and another , some of the ultrasound gets reflected back
the time it takes for the refelctions to reach a detector can be used to measure how far away the boundary is .
117
what are two things ultrasound can be used for
medical imaging
ultra sound waves can pass through the body , but whenever they reach a boundary between two different media some o fthe wave is reflected back and detected
the exact timing and distribution of these echoes are processed by a computer to produce a video image
no one knows if it is safe in all cases
industrial imaging
ultrasound can be used to find flaws in objects such as pipes or materials such as wood or metal
ultrasound waves entering a material will usually be reflected by the far side of the material
if ther is a flaw sucha s a creack , the wave will be reflected sooner
118
what is echo sounding
uses high frequency sound waves
used by boats and submarines to find out the depth of the water they are in or to locate objects in deep water
119
what do we use to detect seismic waves
seismometers
120
what do seismologists do with seismic waves
worko out the time it takes for the waves to reach each seismometer and note which parts of the earth dont receive the shock waves
121
what happens when a seismic wave reaches a boundry between layers of material in the earth
some are absorbed and some are refracted
the ones refracted change speed gradually resulting in a curved path
when prperties change suddenly the wave speed changes abruptly and the path has a kink
122
what are the 2 types of seismic waves
p waves
they are longitudinal
tracvel through solids and liquids
travel faster than s waves
s waves
transverse
cant travel through liquids or gas
slower than p waves
